A seat has a seat cushion unit including: a seat cushion frame; a seat pad which lies over the seat cushion frame; and a trim which covers the seat pad. The trim includes: a trim main body which mainly covers a top surface of the seat pad; a first trim joiner which extends from the trim main body to a backside of the seat cushion frame at the rear of the seat pad, and is fastened to the seat cushion frame; and a second trim joiner which is connected to a back surface of the trim main body in at least one of left and right end regions of the rear of the seat cushion unit, extends to the backside of the seat cushion frame at the rear of the seat pad, and is fastened to the seat cushion frame.