The disclosure describes a double folding type of seat, wherein a panel for at least a seat cushion is molded in a synthetic resin material, and at the same time, hinge male parts of the hinge mechanisms are formed integrally into the molded cushion, and thus decreases the number of parts, reduces the weight, and improves the assembling performance. In particular, the seat includes a reinforcement panel 4 for a seat cushion 2 or seat back 3 being molded in a synthetic resin material, and additional parts for the reinforcement panel being integrally formed.