To seat two infants in a space for oge adult and to protect the infants from a shock of an air bag by providing two seat main bodies in parallel on a frame fixed on a seat of a vehicle by a seat belt and arranging a roll bar between both of the seat main bodies.

A child seat 1 is constituted of a frame 4, two large and small seat main bodies 2, 3 installed on the frame 4 and a roll bar 7 arra arranged between both of the seat main bodies 2, 3. The frame 4 is placed on the seat of a vehicle and a seat belt equipped on the vehicle is fixed by inserting it from a belt insertion port 5 to install the child seat 1 on the vehicle. Additionally, an arm is revolved upward by operating an intermediate clamp device of the roll bar 7 so as to seat an infant in the child seat 1. Additionally, it is possible to protect the infant from a shock at the time of actuating an air bag in the case of installing the child seat 1 on an auxiliary seat with the air bag.