Basic rules of the Road
Cyclists ride on the left hand side of the road.
Riding dangerously, failing to stop at a stop light, or riding with broken brakes carries a maximum penalty of a ¥500,000 fine and/or three months in prison.
Biking under the influence of alcohol is forbidden and carries a maximum penalty of five years in prison and a ¥1,000,000 fine.
Cycling on sidewalks is forbidden, except where indicated by shared sidewalk signs.
An overview of traffic law as well as a guide to Japanese traffic signs can be found here (pdf). Alternately, there is a very thorough guide to the rules of the road that can be purchased through the Japanese Automobile Foundation.
All bikes are required to have a bell and a headlamp (if riding at night)
It is illegal to ride tandem bicycle (except in Nagano) [Read more about the tandem riding rule]
Also illegal (and in line with the previous): riding with a passenger (with the exception of a child below the age of six). Double riders could face a ¥500,000 fine
A cyclist may carry one child under the age of six in a designated child seat
Children under the age of 13 years must wear a bike helmet
Bicycles must be registered in the owner’s name at the prefectural police department