A seat includes a seat frame, and a cushion material supported by the seat frame and having a three-dimensional knitted fabric which is formed by joining, with connecting threads, a pair of ground knit fabrics which are disposed so as to be separated from one another. The cushion material includes a first region whose elastic compliance when a reaction force is applied to an extending side of the cushion material when an occupant is seated on the seat is substantially equivalent to an elastic compliance of a portion of the occupant's body pressing the cushion material and a second region whose elastic compliance is larger than that of the first region. Accordingly, a thin and light seat can be provided, load concentration on the occupant's tuber ishiadicum bottom portion when seated for a long period of time can be mitigated, and vibration-transmitting characteristics can be improved.