To provide a child seat capable of fixing the body of the child seat strongly to a vehicle seat.

A seat belt threading part extending transversely is provided in the lower part of the body 2 of child seat, and the surface of threading part 9 where a seat belt abuts is chamfered. The chamfer consists of a plurality of straight lines or arcs of circle or a combination thereof, or the whole surface is swollen upward in an arc shape. The rear surface of seat belt threading hole viewed on the cross-section is swollen forward in an arc shape, while the ends of the bottom surface of the seat belt threading hole on the longitudinaly cut front view are curved downward in arc shape, and the bottom surface of the seat belt threading hole on the longitudinaly cut side view is curved concave while the rear surface is curved upward in an arc shape.