To prevent a child from receiving great shock at the time of the collision or sudden stop of the vehicle.

A child supporting element 1 supporting a child in a state where the child is seated turning backward to a vehicular traveling direction, is mounted in the vehicle through an installing member 17 so as to freely rotate in a vertical direction about a rotation center 15 such as a front portion 1a or a portion near the front portion 1a of the child supporting element 1. A spring 23 is arranged between the child supporting element 1 and the installing member 17 or the vehicle. The child supporting element 1 supporting a child is kept at a specified angle by the spring 23 at normal times, but is made to rotate in a direction wherein a rear portion 1b of the child supporting element 1 descends against the force of the spring 23.