To secure sitting comfort with simple configuration even if a pad member is thinned.

A support structure 41 for supporting the pad member includes a pair of resiliently deformable rod-shaped members 43, 45 disposed with a space in a width direction along a back and forth direction, and a cloth-like support member 51 laid stretched over the pair of rod-shaped members 43, 45. The support structure 41 is configured to support the pad member in the surface shape of the cloth-like support member 51, to regulate the rod-shaped members 43, 45 in displacement of front ends 43a, 45a and rear ends 43b, 45b approaching each other, and to permit the cloth-like support member 51 to receive the load of a seated person to bend downward by the resilient deformation of intermediate parts 44, 46 to bend in the mutually approaching direction. The pair of rod-shaped members 43, 45 are disposed so that the buttocks of the seated person in the seated state of the seated person is in a position state in which the pair of rod-shaped members 43, 45 can be brought closest to each other.