Koichi Yokomizo graduated from Toho High School Music Department and graduated from Toho Gakuen University. While still in the high school, he was selected for the 58th All Japan Student Music Competition Tokyo Tournament.
At the 14th Japanese Classical Music Competition, he won the 5th place in the national competition of the stringed instrument section of high school students. (At this competition, the 1st and 2nd places were vacant).

Received the highest prize in the high school section of the 2nd Legacy Violin Competition. At the same time, He received the Saitama Central Rotary Club Award. In the field of chamber music, he completed the chamber music examination in the school at the top in 2006 and 2007 and appeared in the chamber music concert and the Hamamatsu Act New Artist Series. In 2006, he formed the Verus String Quartet, received a grant from the Matsuo Science Promotion Foundation as a viola player, and participated in the “Norfolk Chamber Music Festival” at the Yale University Summer Academy in the United States at the invitation of the Tokyo String Quartet.
In the string quartet section of the 57th ARD Munich International Music Competition, we won the 3rd place for the first time in 38 years since the Tokyo String Quartet as a group consisting only of Japanese people.
He has participated in Ravenna Music Festival Miyazaki International Music Festival, Beppu Argerich Music Festival, Saito Kinen Chamber Music Study Group, Saito Kinen Festival in Matsumoto.

Koichi Yokomizo was a concertmaster at the Seiji Ozawa Music Academy Opera Project and Orchestra Project, and a soloist at the Beppu Argerich Music Festival. He appeared as a violist on NHK-FM Recital Passio and was well received. He has studied under Yukiko Ogawa, Takumi Komoriya, Masafumi Hori, and Tsugio Tokunaga. He studied chamber music under Tsugio Tokunaga, Hakuro Mori, Koichiro Harada, Kazuoki Fujii, Yoshiko Kawamoto, Leipzig String Quartet, Mathias Tacke, András Keller, and Tokyo String Quartet.
He left Verus String Quartet in 2009 and returned in 2013.
He has also performed with famous musicians such as Richard Stoltzman, Paul Meyer, Clemens Hagen, Mayuko Kamio and Fumiaki Miura.
Currently, in addition to his activities as a vice principal of 1st violin of the NHK Symphony Orchestra, he is also a guest violist in various orchestra.