A 60-year-old Japanese man switched at birth says he would like to "roll back the clock", days after winning a lawsuit against the hospital that mistakenly cast him into a life of poverty.

The man told a packed Tokyo press conference that he was shell-shocked when he learnt the truth, saying his life would have been starkly different.

"I've wondered how on earth could this happen. I couldn't believe it. To be honest, I didn't want to accept it," he told Japanese media late on Wednesday. The man was not identified.

"I might have had a different life. I want (the hospital) to roll back the clock to the day I was born."

A Tokyo district court this week ordered the hospital to pay Y38 million ($A411,100) in damages over its 1953 blunder which saw the man switched with another baby boy who was delivered just 13 minutes later.