It depends on what you are trying to do, but I managed on about that comfortably. If you have sorted out things like a rail pass and such before hand then should be fine. Backpackers I stayed in were like $30 US for a bed in a dorm room, and generally I was paying < $10 a meal. More interesting food can often cost more of course. Most of the things I went to see didn't cost much to get into, biggest costs that aside really were transport. almost 8 years ago
I reckon that'll be ok. No doubt accommodation will be the biggest slice of this. If you are planning on traveling around a bit, buy a japan rail pass BEFORE you arrive in japan and it's much cheaper! http://www.japanrailpass.net/eng/en001.html
Food is one of the great surprises of the country: both supremely delicious and very economical. almost 8 years ago
It will totally depend on what you have planned.
I found public transport was the most expensive part of my recent trip and it pays to pay a little bit extra for better food.
But with the current conversion of 100.00 USD = 8,861.05 JPY that would be pushing it to really enjoy the country in my opinion.
But saying that it all depends how much you want to dirt bag it....
If you go to the supermarkets before closing you can pick up a super tasty lunchbox on special for about $3 and a 500ml beer for about $1.80. almost 8 years ago
I worked out that 10000Y/day was enough to live VERY comfortably in Japan. I would recommend having a 10000Y note for each day you are there and you won't have to worry about getting cash out. It is really hard to find an ATM in Japan. They are not convenient at all. Alot of places don't have EFTPOS either. A really good meal for dinner with a drink or 2 might cost you 1000Y-3500Y. Depends how much you want to drink. Then entry to attractions really doesn't cost that much at all maybe you might spend 0-2000Y/day. I think realistically you could get by with less Y/day maybe 6-8000Y (which is about what i spent), but i found it soooooo convenient just knowing that I could whip out a 10000Y note for the day (unless i had Y left over from the previous day) and I NEVER needed to get cash out once from an ATM.
****** This answer of course assumes you have already paid for JR Pass and accomodation. But my 10000Y/day did cover me to order what ever i wanted on dinner menu, dessert, non JR public transport, entry to usual touristy things.*****
Hope this helped you -- Have fun Japan is awesome almost 8 years ago