Born in Tokyo, Japan on October 12 1946 as a son of a jazz band leader and pianist, Yoshiaki Masuo grew up surrounded by jazz music, although he never had any formal musical training. At the age of 15, he started playing the guitar on his own. Prominent among his early influences were Wes Montgomery and Grant Green.
While in Waseda University Jazz Club, Masuo was discovered by alto saxophonist Sadao Watanabe, and joined his group at the end of 1967. Masuo thus started his professional career on top as a regular of Japan's leading jazz group. He was in the group for three years, and experienced tours outside of Japan with Sadao, playing at Montreux and Newport jazz festivals. He was 1970's number one guitarist in the readers' poll of Swing Journal, Japan's most popular jazz magazine. He won the readers poll in the following years even after leaving Japan, five times in total.