Akitoshi Igarashi (五十嵐明要, Igarashi Akitoshi in Japanese order) was born on 2 June 1932 in Hatchobori, in Tokyo's Chuo ward, the youngest of five children. His family ran a neighbourhood variety hall, a yose called Bunrakutei, and his elder brother Taketoshi (五十嵐武要) became a drummer. In 1944 he was evacuated with his school to Omiya, north of Tokyo, and in 1945 he came home to sit middle-school entrance exams and live through the Tokyo air raids. In the summer holidays of his first year of high school, 1948, he took a job as a band boy for a hotel band at the Marunouchi Hotel, and that was how he got into jazz.

He began on clarinet. A saxophonist in his brother's band, who later married his sister, urged him to take up the saxophone, but the clarinet came first. In 1949 his bandleader sent him off with a man who turned out to be Hitoshi Ueki, later of the Crazy Cats, to stand in for a week at Club Eden, next to the Kabuki-za in Ginza. Ueki then asked whether he would like to stay, and Igarashi played in the club's Dixieland-style band for several years, which counts as his professional start. Around 1951 the drummer Akitaka Matsushita, whose bop-minded Metro Tones played at the Foreigners Club on Dogenzaka in Shibuya, told him he could join if he played saxophone. Igarashi sold his clarinet and bought an alto. He recalls in a 2015 interview that the teenage Sadao Watanabe used to listen from outside the club's glass window and that, at the midnight jam sessions, he told the boy to come up and play; Watanabe took out his clarinet and was good.

In the early 1950s he played in guitarist Shungo Sawada's Double Beats Five, one of the first Japanese jazz combos, alongside his brother Taketoshi, working Ginza clubs and playing Charlie Parker's repertoire. A Swing Journal photograph from August 1954 shows the band with the pianist Shotaro Moriyasu. That July, on the 27th and 28th, he took part in the all-night jam session at the Mocambo Club in Yokohama that was taped and later issued as the Historic Mocambo Session '54. It was his first recording. The complete edition credits him on alto on "Steeple Chase" and "Perdido" (with Moriyasu, Watanabe and the other altos), on "Taking a Chance on Love" with Toshiko Akiyoshi on piano, and on a ballad medley. The tenor saxophonist Akira Miyazawa is also on the date.

Big bands and West Coast-style small groups took up the next decades. He joined Kenzo Takami's Midnight Sons in 1956 and in 1957 Konosuke Saijo's West Liners, which at that point had Norio Maeda on piano and Tadayuki Harada on baritone. When his brother left the West Liners' drum chair, Takeshi Inomata took it and eventually led the band. In 1958 he is among the billed names on King's Latin Carnival with the Tokyo Cuban Boys, alongside Hidehiko Matsumoto and Hideo Shiraki, and in October 1958 he played in the Swing Journal All-Stars poll winners' concert issued as Jazz Festival of Japan. In 1960 he joined Nobuo Hara's Sharps & Flats and stayed about ten years, until the work had become mostly accompanying singers of popular songs and he decided he had not taken up the saxophone for that. In 1967 he moved to the Blue Coats, led by Shigenori Obara and later by Toshio Mori, as lead alto and concertmaster for roughly a decade. The band's Billy Strayhorn and Tadd Dameron albums of 1976 to 1978 list him. In 1978 he moved to Obara's New Otani Joyful Orchestra, and that year he and his brother formed their own group, The Bunrakutei, named after the family hall.

Alongside the section work he made records for the Japanese majors. Columbia issued Oyasumi Mae No Hitotoki (1961), alto-sax mood music with the Columbia Salon Strings, and Anata to Yoru to Alto Sax (1964), with strings and arrangements by Norio Maeda, Kiyoshi Yamaya and Osamu Onishi; Victor issued Fascinating Alto-Sax Vol.2 (1968) under the name Akitoshi Igarashi & Dreamy Sounds. His small-group jazz work from the period includes the Takt album 5 Saxophones (recorded November 1967, with Maeda, Inomata, Miyazawa and Saijo), the 1974 Trio Records session Smoke Rings with the pianist Yuzuru Sera and Eiji Kitamura on clarinet, the 1975 Alone Together for Audio Lab, recorded on 6 June 1975 with Inomata, Maeda, Saijo, Harada and the trumpeter Tetsuo Fushimi, and the West Liners albums of 1977 and 1978. He is the alto on Martha Miyake's This Is Martha (1978) and, in 1976, on Toshio Oida's It Was A Very Good Year for Three Blind Mice.

In 1986 he recorded Sax Talk, which his official website lists as his first album as leader. Recorded on 21 October 1986, it is a nonet with Nobuo Tanabe on tenor, Tetsuo Fushimi on trumpet, Tomoaki Hashizume on trombone, Toshihiko Ogawa on piano, Sadanori Nakamure on guitar, Kunimitsu Inaba on bass and Taketoshi Igarashi on drums. Swing Time followed in June 1988, a sextet session with the pianist Yoshitaka Akimitsu and the vibraphonist Ichiro Masuda, cut at Pioneer Studio in Meguro for the audiophile GML label as a 24-karat gold disc. In 1992 he was the first alto on Masuda's NHK-FM Live Session '92 big band set with Saijo, and in 1995 he made Here At Last with the Yoku Tamura Trio and the guitarist Toru Konishi. In 1998 he cut the quintet albums All Of Me and Satin Doll with his brother, and in 1999 Battle of Sax with the tenor saxophonist Jun Sugihara and Tadayuki Harada.

His reputation travelled. His official website records that he was invited to the Monterey Jazz Festival in 1989 as a representative of Japanese jazz, played the Los Angeles International Jazz Festival with Eiji Kitamura in 1992, appeared at the Apollo Theater and Carnegie Hall in New York in 1994 as a member of the Japan Just Jazz All Stars, and played the Breda Jazz Festival in the Netherlands in May 2001. In 2004 he formed the Yokohama Royal Park Orchestra with the drummer Isamu Harada. In 2012, with Sugihara and Harada, he started the three-saxophone group KKB, short for kōki kōreisha band, a joke on the idol group AKB: the three players' ages added up to about 240. Sugihara passed away in December 2018.

Official recognition came late. The Japan Jazz Music Association honoured him in 2017 (its Jazz Grand Prize, according to Japanese Wikipedia), in January 2018 he received a commendation from Japan's Minister of Education, Culture, Sports, Science and Technology as a leading jazz alto saxophonist who had contributed to the country's musical culture, and in October 2020 the association gave him its Honorary Chairman's Award. His 80th birthday was celebrated at a party in June 2012, and a 92nd-birthday session with friends was held at the Tokyo club Satin Doll on 26 June 2024. He turned 94 in June 2026, and his official website, still maintained in 2026, lists him as active with a schedule of club dates in Tokyo.

Igarashi plays in a swing-based mainstream style, closer to the saxophone sections of Duke Ellington and Count Basie than to bebop. Nobuo Hara, in a piece on the official website, calls it a middle-road style, neither ultra-modern nor old, and says nobody beats him at playing swing or matches the beauty of his alto tone. The critic Masahisa Segawa titled his review of him as the number-one alto player in the country, and Sadao Watanabe wrote that as a young man Igarashi was one of the stars he idolised.

By Igarashi's own account the tone is the thing. In the 2015 Sax Magazine interview he says the first time he heard Johnny Hodges' solo on an Ellington record he decided to chase that sound for life, which is also why Charlie Parker never quite fitted him, although in the early 1950s no Japanese saxophonist could admit that. He also says his method is to pick a player and immerse himself in that style for months or years: Paul Desmond, Art Pepper, Bud Shank and Lennie Niehaus each had a turn, and Norio Maeda's West Liners arrangements often carried Niehaus' nuances, which suited the exercise. In the Sharps & Flats and the Blue Coats he learned to play lead alto, reading new charts at sight and keeping the section's pitch, and later passed that on as a section leader. His working repertoire runs from swing standards and Ellington and Strayhorn through cocktail and dance music.

Part of his catalogue is mood music rather than jazz: the 1961 and 1964 Columbia string albums and the Victor Dreamy Sounds LP are lush, easy-listening alto records, and for much of the 1960s he spent time backing singers in big bands. Most of his documented work, though, is jazz of the swing and mainstream kind, and that is where his reputation rests. His main horn is a gold-plated Selmer Mark VI, played on a Meyer 5 mouthpiece with Rico 2 reeds.