Gihei Oka (30 January 1883 - 20 September 1991) was a Japanese centenarian and Japan's oldest living man from the 18 June 1991 death of Shimetaro Hara until his own death on 20 September 1991, aged 108 years, 243 days. He resided in Tochigi prefecture. He was succeeded as Japan's oldest man by Gengan Tonaki.