Tokyo Mansion

Probably the smallest apartment (known as a Mansion) I've seen in the 10 years I've lived here. Comrades at Akihabara News go looking for an apartment and was introduced to this place.
You need to check out the video to see just how small it is.

The rent is 50,000 yen for a month. Notice how the shower unit is not even separate from the toilet.

You can however get places for a decent size from 55,000 yen on the Yamanote line - this search result lists a few places - one even has 3 rooms but 18 mins walk from the station. The further you are prepared to walk from the station, the cheaper the rent will be.

This photo article has pics of all my previous apartments that I've lived in since I got to Japan and how much I paid for rent.