A seat includes a seat cushion frame, a seat back frame mounted to the seat cushion frame, and at least one three-dimensional net having upper and lower mesh layers and a pile layer made up of a large number of piles for connecting the upper and lower mesh layers. The three-dimensional net is stretched over substantially the entire region of the seat cushion frame and the seat back frame, thereby forming a seat cushion and a seat back. The three-dimensional net has a fixed end at a front end portion of the seat cushion and another fixed end at an upper end portion of the seat back. The seat also includes a first tension member attached to the three-dimensional net at a location adjacent to a central portion thereof for imparting tension thereto, and a second tension member attached to another portion of the three-dimensional net for fastening it to at least one of the seat cushion frame and the seat back frame.