It's somthing that is particularly hard to get information on. The man on the scene (Japan Channel man ) mentioned he brought 25,000 Austrailian dollars with him when he first came to Japan, which for my currency is about 20,000 euros (so its ALOT of money). So there possibly may not be such a problem with a cash or currency limit for Japan.

Having said that, you will possibly have to declare your cash by customs when you arrive (I think you have to in most countries if your cash is over a certain amount).

Id say send an e-mail to your own country's Japanese consultate and just ask them. They will possibly have a better answer