To prevent hips and thighs from being pressed more than necessary by reducing a load on the hips and thighs of a seated person, to improve cushion property, touch and sitting feeling, to improve air-permeability, to reduce a weight and to improve assembling work performance by dispersing with a pad material.

A skin material 25 is formed of structure woven sheet consisting of a front surface ground fabric 26 and a rear surface ground fabric 27, and an elastic intermediate layer 28 woven/knitted integrally with the front/rear fabrics 26 and 27. The skin material is formed of a skin material 35 on a front surface side and a skin material 25 on a rear surface side. The material 35 on the front surface side is formed of a member of more flexibility and cushioning property compared with the material 25 on the rear surface side. Forming members 31 in the shape of a cord are put through the intermediate layer of the part, of the skin material 25 on the rear surface side so as to form the part in a desired shape.