Abstract: A seat cushion 17 is provided with a seat portion 17a, a back portion 17b provided so as to be continued to the seat portion 17a, and a leg-pad portion 17c. A get-out preventing cloth 17e is sewn onto the leg-pad portion 17c. The get-out preventing cloth 17e is sewn onto not only the front end but also the left and right sides of the leg-pad portion 17c. At the inside front portion of each of arm-rest cover portions 17d, a pocket 17f is provided in a state where the pocket 17f is opened at its rear end, and hook and loop fastener 24 is stuck inside the pocket 17f. A second crotch belt through hole 17n is formed in a suitable position of the get-out preventing cloth 17e so that a crotch belt 14 is inserted through this crotch belt through hole 17n.