To provide a lightweight and inexpensive seat having cushioning property and durability by integrally molding a resin by blow molding to constitute the seat, and providing an elastic cushion part in the contact part with an operator and a compression part between a sitting part and a seat back part.

This seat 450 constituting a driver's seat consists of an integrally molded product by blow molding, and a highly elastic cushion 451 is adhered onto a sitting part 450b on which an operator directly sits by an adhesive. A cushion part 450f having proper elasticity is formed in the part directly making contact with the body of the operator of a seat back part 450a. Further, the surface and reverse sides of the connecting part between the sitting part 450b and a seat back part 450a are mutually pressed and connected to provide a compression part 450n. According to this, the contact part of the seat 450 with the operator can be provided with impact absorbing performance to significantly improve the riding comfortableness, and the rigidity of the whole seat can be also improved.