Junya Koga (古賀 淳也 Koga Junya, born July 19, 1987 in Kumagaya, Saitama) is a Japanese backstroke swimmer. He is a Waseda University student in Tokyo.
In May 2009, he set the Japanese records in the 50 m and 100 m backstrokes at the 2009 Japan Championships, qualifying for Japan's team to the 2009 World Championships.
In long course
- 50m backstroke 24.24 Asian record (August 1, 2009)
- 100m backstroke 52.26 (July 28, 2009)