This event is held every first Sunday of April every year. This can be changed and by 2012 it was on Sunday, April 1.
The place where it happened is Kanayama (金山 神社) in Kawasaki, near Tokyo itself. The main theme for this matsuri is surely the pink penis statue parade, dress up in various costumes and sculptures, talisman, snack and candy made specially for this.
The matsuri is about the faith that to get married, good living and also having a full house. Also the prostitute who wish to be safe from the disease.
In the ancient world also believe that the devil is in the sexual abuse of women and men in marriage. So they must pray to not see the devil that is the source of the iron with a penis made in order to exorcise the demons. At the present, this is also the funding of AIDS research and treatment :).