St Patricks's Day is celebrated on the 17th of March, but that's not a good day for a parade, so this years parade was on Sunday 15th.
It's the biggest Irish event in Japan and it was started in 1992 to introduce Ireland to Japanese people. (And to give all the expat Irish an excuse to walk down the middle of the road.)
The parade in Japan is organised by the Irish Network Japan, and if you missed the Tokyo one there's still time to catch one in Yokohama and Nagoya on 21st Mar and Tsukuba 28th March.
A few more photos of the fun on flickr