Junji Hirose (広瀬淳二) was born on March 29, 1955, in Kokubunji, on the western side of Tokyo. He came to jazz in junior high school through Miles Davis and Terumasa Hino, bought a trumpet and taught himself to play it, and later, after hearing John Coltrane, bought a tenor saxophone and taught himself that too. He took up the soprano around 1977. He entered Meiji Gakuin University in 1973, joined its modern jazz club, and graduated in 1978; his first record appearance came while he was still a student, on a recording by a soul group.

The student years also gave him his direction. Alexander von Schlippenbach's trio album Pakistani Pomade, with Evan Parker and Paul Lovens, was his first encounter with European free improvisation, and in 1979, about a year after graduating, he formed a free-improvisation trio of his own, Free Expansion, with Shuichi Nagano on bass and Yasuhiro Yamazaki on drums. His first solo album, Solo Saxophone, was recorded live in two sessions at the Far-Out club in Atsugi, Tokyo, on July 21 and August 18, 1980, and issued on the small Cacoon label as CACOON-001; Hirose produced it and did the layout himself. Hodgepodge (Cacoon, 1982) followed, built from four 1981 recordings with Nagano and Yamazaki and the guitarist Akira Iijima, and in 1984 he made Chi-Chi-Chi-Nngacah with Yoshinori Motoki, a record on which he plays electric guitar, percussion, toys and remodeled junk rather than a saxophone.

In 1982 he joined the EastAsia Orchestra, the free-jazz big band led by Yoshiaki Fujikawa. He is credited on reeds on its Shoyoh Jurin, recorded on March 14, 1983, and he rejoined in 1984 for a European tour of Germany, the Netherlands, Switzerland and Austria; the orchestra's set at the Volksbühne in East Berlin on June 17, 1984 was released as Jazzbühne Berlin '84. That same year he began a long association with Masahiko Togashi, playing in the percussionist's duos, trios, quartets and orchestras until Togashi passed away in 2007. His tenor is on the Improvisation Jazz Orchestra's Follow the Dream, recorded live at Sogetsu Hall on November 7, 1984, on Togashi's Essence of Jazz, cut at Sunrise Studio in Roppongi on December 9 and 10, 1987 with Hirose on tenor and soprano, and on the Inter-Action live set from Hall Egg Farm on December 9, 1995.

Through the second half of the 1980s he was also building an instrument. Starting in the mid-1980s he assembled what he calls the SSI, a self-made sound instrument put together from bicycle wheels and other everyday objects, with pickups that amplify the sound of hitting and scraping them; a smaller version made in 1987 became the prototype for the later ones. He began playing duos with Otomo Yoshihide in 1988, and their LP Silanganan Ingay was recorded live, with no overdubs and no edits, at Space Alta in Yokohama on April 28, 1989. Hirose is credited on tenor saxophone, autoharp, toys and self-made instruments, Otomo on turntables, cassette tape and a hand-made guitar. In 1988 he appears on Ort Live: Brecht A La Machina, credited with soprano and tenor saxophone and instruments, as part of the group 機械じかけのブレヒト (Kikai-jikake no Brecht), and from 1989 he sat in occasionally with the large collective Shibusashirazu, on whose Dettaramen (recorded January 1992) and Shibusamichi (recorded December 1993) he is credited on tenor and soprano or sopranino saxophone.

The early 1990s were a crowded stretch. He played with Otomo's band Ground-Zero as a guest in 1991 and as a regular member in 1992 and 1993, and he was in the band's final Tokyo concert in 1998; he is credited on tenor and soprano saxophone on the 1993 album Ground Zero. From 1991 until 1999 he was a member of drummer Masahiro Uemura's instrumental band P.O.N., on whose 1995 album he plays saxophone and a noise machine. In the mid-1990s he joined Hideaki Sasaki's trio project Stereodrome, alongside Kazuhisa Uchihashi, and he is reported to have played the Moers Festival in Germany in 1993 and 1998. On June 12, 1995 he recorded a quartet set at Romanisches Café in Roppongi with the Korean trumpeter Choi Sun Bae, the bassist Motoharu Yoshizawa and the Korean percussionist Kim Dae Hwan; NoBusiness Records issued it in 2018 as Arirang Fantasy.

His solo saxophone work was documented again on The Elements - Tenor Saxophone Solos (DoubtMusic, 2010), seventeen unaccompanied pieces recorded at Knuttel House in Tokyo between October 2009 and June 2010. From 2013 the noise instrument got its own series of releases on the Hitorri label: SSI-4, a live set from Ftarri recorded on January 27, 2013, then SSI-5 (2015), SSI-6 (2016) and SSI-7 (2020), each documenting a new version of the instrument, with No-Instrument Air Noise (2017) removing the instrument altogether and pointing air compressors at microphones. Alongside them came a run of duo and trio records, among them Saxophonedaxophone (DoubtMusic, 2015) with Kazuhisa Uchihashi on daxophone, Foreign Policy (Lao Ban, 2019) with Toshimaru Nakamura and Darren Moore, and Duo-1 (Ftarri, 2022), a live recording from the Tokyo space Pool that reunited him with Otomo Yoshihide more than three decades after Silanganan Ingay. In 2022 he and Otomo also joined the guitarist Takayuki Kato and the drummer Masataka Fujikake on Ten-Shi III, recorded at Pit Inn in Shinjuku.

Around 2021 he began presenting the SSI as a recurring series at Pool, and when the series was suspended in May 2024 he recorded five audience-free performances there, on July 13 and October 6 of that year, which Ftarri issued as SSI Solo 2024. His latest tenor saxophone records are with the guitarist Kazuo Imai: Be Quiet!!! (Meenna, 2023), a trio with Darren Moore recorded on August 4, 2022, and Go Home and Go to Bed !!! (Ftarri, 2024), a duo recorded live at Ftarri on December 11, 2021. He turned 71 in March 2026 and was still performing in Tokyo that spring, in a tenor, bass and drums trio at Velvet Sun in Ogikubo on May 21, 2026.

Hirose works in free improvisation, and Discogs files most of his own albums under Jazz with the style tag Free Improvisation. The saxophone playing draws on the two sources his own biography names: Coltrane, who led him to the tenor, and the European free improvisation he first heard on Schlippenbach's Pakistani Pomade. The Elements - Tenor Saxophone Solos shows the solo side of that tradition, seventeen unaccompanied improvisations numbered rather than titled, some barely a minute long and some past six.

The second half of his work sits outside the saxophone altogether. The SSI is an acoustic noise instrument in the sense that nothing is synthesized: bicycle wheels, plastic strings, glass and plastic bottles, brushes, rubber bands, washboards and metal trays are hit and scraped, and installed pickups turn that into dense layers of sound. The titles on SSI-6 are simply the materials. His later air-noise pieces use compressors to blow air onto microphones, producing what the label describes as explosive sound. This puts him on the noise side of the Japanese improvised-music scene, close to Otomo Yoshihide's circle, as well as on the jazz side, and his catalogue crosses between the two: Discogs tags the SSI releases variously as free improvisation, experimental, and non-music.

What ties the two halves together is the stage he works on. Most of his records document live rooms: Far-Out in Atsugi, Ftarri and Pool in Tokyo, Pit Inn in Shinjuku. He is as likely to be heard against a tuba, a daxophone, an electro-bass or a no-input mixing board as against a conventional rhythm section, and he has been recorded in each of those settings.