Yoshio Shinozuka, 79, a former member of the Japanese army's notorious Unit 731, said the Japanese administration had the chance to admit culpability at a ruling on the issue in a Tokyo court next month.
About 180 Chinese are suing Tokyo after they say their relatives were killed in biological warfare and human experiments carried out by Unit 731 in the 1930s and 1940s.
Mr Shinozuka, who said he considered himself to be a war criminal, described the 27 August ruling as "a crucial test for Japan's conscience".
Dehumanised
The army veteran told correspondents in Tokyo that the programme's human guinea pigs were referred to as "logs".
"We said we have chopped one log, two logs," Mr Shinozuka said.
He and other Japanese veterans have testified in court that they mass-produced cholera, dysentery, anthrax and typhoid in Harbin until 1945 to use mostly against prisoners of war and the Chinese people.
Historians believe that the unit may have killed as many as 250,000 in their experiments.
"I have done what no human being should ever do," said Mr Shinozuka.
Apology 'unlikely'
The Japanese Government had acknowledged that Unit 731 existed but has refused to confirm the soldiers' accounts.
Mr Shinozuka said recent precedents indicated that Japan was unlikely to apologise.
"There is a very clear trend now to admit facts but to reject an apology for the facts," he said.
"But if you admit that you have done something wrong, you apologise. That is the way a man should live."
Although Japanese courts in recent months have ruled in favour of plaintiffs used as wartime labour suing private companies, no such case against the government has succeeded.
The 1951 San Francisco Treaty which officially ended the war between Japan and the allied forces ruled out subsequent individual claims for reparation.