An Australian man detained for more than 40 days and convicted of illegally entering an apartment building in Tokyo said he was trying to find out the location of his children, who were taken by their Japanese mother.

The case has drawn wide attention to the difficulties in Japan faced by parents who lose access to their children after their partners take them away.

While the family was living in Tokyo in May last year, Scott McIntyre's wife told him she was taking the children to stay with their grandparents.
The 46 year-old has not seen them since.

The children were removed from their school, their phone numbers changed and their mother switched her email address.

"I've been refused any access. I'm not allowed to speak to the child. I'm not allowed to know what school they're attending. I'm not allowed to know if they're alive or dead," he told the ABC.

Mr McIntyre said he had made numerous requests to the police and his wife's lawyers — the two are going through a divorce mediation — to let him know whether the children are safe, but the requests were ignored.

In October, he said in the aftermath of a devastating typhoon in Japan, he trespassed into the common area of his estranged in-laws' apartment complex trying to find more information about his kids.

He said he had followed another resident inside, checked to see if there were any of his children's things outside the door of his in-laws' apartment and left.

A month later he was arrested and put into detention for 45 days, with the lights on 24 hours a day.

"[The constant light] makes everybody walk around like a zombie," he said.

"You're not aware of your own thoughts — you don't have clarity in thinking.

"I was interviewed on every occasion without a lawyer being present.

"I was held with several murderers, an armed robber, a rapist, a paedophile and several gangsters."

In the Tokyo District Court, he received a six-month jail sentence suspended for three years.