To enable child-seat that is possible to be mounted on a seat of a vehicle to be used also as a seat of a baby buggy by detaching it from the vehicle seat.

A pushing member 15 and a leg part 16 are systematically moved so that each will be housed at a back plane of backrest 12 and under surface of a seat part 11, and a child-seat 10 is mounted on a seat 18 using a seat belt that is equipped with a vehicle. To use the child-seat 10 as a baby buggy, since the seat part 11 is supported on the floor or the ground top by the leg part 16, and further, since a wheel 16a interveningly exists between the leg part 16 and floor or the ground, a person who grips the tip end that has been wound of rubber 15a can let the child-seat 10 move with a small force by pushing the pushing member 15 under the condition that an infant or baby is fixed using a belt 13.