Flea market is not so popular in Tokyo, rarely you are able to find them. But, there is one big flea market in Shinjuku, just in front of the Tokyo Metropolitian Government Building in Shinjuku Central Park.
The flea market operate every Sunday, and they are huge variety of items sold, ranging from second hand cloth, antiques, collectible items and cute cute stuff for girls! It is very busy and crowded.with family and students. You can see lots of cute little girl running around and young girls hunting for a good bargains!