In cities (even large Tokyo) and towns, many, many people get around on bicycles. And especially in cities, they ride their bikes not on the road but on the sidewalk/footpath.
The photo shows a rare part of Tokyo in which there is actually a sign showing which side the bikes should ride on and which side pedestrians should walk on. Usually there is no sign. And usually there is no convention either – bike riders wander all over.
So you have to be careful just walking around.
Don’t stop walking suddenly or make an unexpected move left or right without checking behind you that there is not a bike fast approaching. (They don’t ring bells or give any indication of approaching).
There are occasional news reports of elderly pedestrians being hit and seriously injured (or killed) by bikes. And because a lot of bike riders are women ferrying babies and young children in front and rear bike seats, there are also occasional reports of death or injury of kids falling to the hard ground if a bike is hit or falls. (Helmets are not compulsory).
Luckily, almost all the bikes are the wide-handled ‘casual riding’ bikes, not racing bikes. And are ridden relatively slowly and carefully.
Japan Tourist Tips 