Loophole in labor law?

[ToshiCG]

I decided to quit my job in a computer graphics company in Japan due to unacceptable working conditions - long hours(around 11hours/day, often longer), unpaid overtime etc. I know that's not unusual for Japan, but it's still unacceptable for me personally.

I am on good terms with my boss so we had a frank conversation about the things I didn't agree with. He then told me that there is a law which basically makes those working conditions legal. Unfortunately, I don't remember the Japanese term he used.

Honestly, I don't believe there is a law that would allow an employer to exploit his people like that but I was wondering if there is some loophole that makes his business at least semi legal.
Again, it's a computer graphics company, I guess that falls under IT. My boss told me that some IT/programming companies also make use of that particular "law".

Any ideas what law he was referring to?