A cushion member includes an intermediate layer, and an upper layer and lower layer stacked and fixed thereto. The cushion member is fixed to a frame by bending an end part of the cushion member so that the upper layer comes to the front side and the lower layer comes to the back side. The intermediate layer is subjected to shear force and the upper layer and the lower layer are subjected to compressive and tensile stress. With the spring characteristic of the intermediate layer, residual stress of the tension and compression is applied to the upper and lower layers from the intermediate layer. Thus, the cushion member can have a restoring property, generation of creases during no load application can be reduced, permanent setting is made less likely, and a compression characteristic in the thickness direction is increased.