[Nyororin]

Japan isn`t 100% crime free. I don`t blame the original poster. It`s always better to be safe than sorry...

On the other hand, you`re going to have a lot of trouble if you try to go about using travelers checks. This was a couple years ago, but I had to help someone exchange theirs, and it literally took all day to find a place that would do it - and even then, they charged a huge fee.
I imagine things are a bit easier in a hugely tourist frequented area like Tokyo, but then again it isn`t as if we were out in the countryside.

I`d say it would probably be easier to invest in a slim money belt, and keep the majority of the cash in it, hidden away beneath your clothes. At the very least, I can say with confidence that the chances of you being held up or robbed are far lower than the chance of simply losing your wallet or dropping the cash.