Its the Suginami Bicycle Festival taking place at Suginami Nisho Mae Hiroba which is along the Zenpukuji River right where it meets Itsukaichi Doori.
My daughters were keen to ride at the Suginami Traffic Park Saturday afternoon, and this festival just a few minutes ride up the river from there, so we'll pop in for a look. If you're in the area why don't you join us?
Images from Tanuki Cycle Blog.