Tadahiro Kosaka (Japanese: 小坂 忠広; born February 10, 1960, in Wakayama) is a retired Japanese male race walker. He competed for Japan at three consecutive Summer Olympics: 1988, 1992, and 1996.
| 1988 | Olympic Games | Seoul, South Korea | 47th | 20 km | |
| 31st | 50 km | ||||
| 1990 | Asian Games | Beijing, China | 3rd | 50 km | |
| 1991 | World Championships | Tokyo, Japan | 13th | 50 km | |
| 1992 | Olympic Games | Barcelona, Spain | 24th | 50 km | |
| 1994 | Asian Games | Hiroshima, Japan | 3rd | 50 km | |
| 1996 | Olympic Games | Atlanta, United States | 29th | 50 km |