A crotch belt (20) which is one component of a body restraint belt includes an elastic plate (21) having bending elasticity, and a buckle (22) mounted on an end of the elastic plate (21). One end of the elastic plate (21) is fixed to a fixing point (23) under a seating surface (4). While the crotch belt (20) is not connected to a waist belt, the crotch belt (20) is positioned along a front part of the seating surface (4) so as to be close to it by elastic force of the elastic plate (21).
