a seat for vehicles having a seat cushion and a seatback includes a seat cushion bracket mounted on both sides of the seat cushion , a seatback bracket mounted on both sides of the seatback , a lever rotatably pivoted on the seatback bracket , a cam member slidably supported on the seatback bracket and operatively connected to the lever , a locking groove formed on the seat cushion bracket and fixedly connectable with the cam member , and urging means interposed between the seatback bracket and the lever and always urging the lever so as to fixedly connect the cam member and locking groove .