He studied with his father and Saburo Sumi, then with Hideo Saito at Toho Gakuen School of Music. He became the youngest concertmaster ever of Tokyo Symphony Orchestra in 1966. In 1968, he went to Berlin to study with Michel Schwalbe under the support of Agency for Cultural Affairs in Japan. In 1976, Tokunaga took up the position of a concertmaster with NHK Symphony Orchestra, and since then, he had been the most well-known representative of this orchestra for many years as a principal concertmaster and later as a solo-concertmaster.

Tokunaga left the NHK Symphony Orch,estra in 1994 and has been dedicating himself to solo and chamber music. He has been the Music Director of JT Art Hall since 1995. He had also been nominated to the General Producer of the Miyazaki International Music Festival in 1996, and has been the Music Director of this festival since 2011. Those positions prove that he has established the most important position in the chamber music field in Japan. Tokunaga is a professor at Toho Gakuen School of Music.