Masayoshi Matsumoto joined the Japanese army in 1943 and went to China as a medical orderly.
One of his tasks was to examine Korean women brought in to work in a military brothel.
"The comfort women had to go for sexual health checks, you could say it was their job to do it -- just as it was my job to check them. There was no choice in the matter. To refuse would have been a death sentence," he said.
Historians estimate that as many as 200,000 so-called comfort women were forced into prostitution by the Japanese Imperial Army during World War Two.
Matsumoto who is 91 and a Christian pastor says it is now his mission to speak out about the injustices suffered by Asian women.
"The Prime Minister should apologise fully and without reservation on behalf of the Japanese nation. And the people that need compensation should be paid. He should beg forgiveness for the things that were done."
The comfort women issue has long been a diplomatic thorn between Japan and South Korea.
Last week the Mayor of Osaka sparked a firestorm of criticism at home and abroad when he said the military brothel system was "necessary" during World War Two.
