An adequate mechanical stiffness and strength are afforded to a tumble seat or a vehicle seat having a latch mechanism provided in a rear end of the seat cushion. A cushion frame (F1) of the seat includes a side frame (5) extending in a fore and aft direction, and the side frame includes a first member (10) comprising a channel member having an open side facing sideways and a second member (11) attached to the first member so as to form a closed cross section jointly with the first member, and extending downward further than the first member. A latch mechanism is positioned under the first member and attached to the second member.