Tandem riding in Japan?

Question:

In many manga's and drama's I see that tandem riding is prohibited in Japan/Tokyo.
Is this true?

Answer:

Yes.
Generally, tandem riding of bicycle is banned by laws in Japan.
It says that only driver can ride on 2 wheels vehicle.

But there are some exceptions. ex. An adult and one small child with child seat is allowed.
And you have to be careful with other prohibitions.