To solve the problem wherein the number of children to be mounted on a general bicycle is determined to one child of aged six and under, but mother in child care mounts two children if necessary, and mounts one child in a seat provided in a rear part of the bicycle and mounts the other on a seat provided in a basket fitted to a handlebar, and it is very dangerous.

In this invention, it is made clear that an infant of aged 2-3 can be safely seated in a space between mother as a driver and a down tube 11 by three-dimensionally observing that space. In Fig.1, knees of a child and knees of mother are overlapped with each other, but the knees of the child are closed by the seat and width of both the knees is about 15 cm, and on the other hand, the knees of mother are opened at about 25 cm to rotate pedals like Fig.2 expresses, and there is no danger of hitting knees against each other, and further, the center of gravity is lowered to increase safety.