Abstract: A locking mechanism comprises a chassis, a floating unit supported movably by the chassis through the intermediary of a damper, a shift plate provided in the chassis and movable by a drive power of a motor, a link mechanism cable of rotational movement by the movement of the shift plate, and a lock plate movable by the link mechanism. The shift plate has a first lock part movable in a first direction, the link mechanism has a second lock part movable in a second direction perpendicular to the first direction, and the lock plate has a third lock part movable in the first direction. The floating unit has first, second and third engaging parts for engaging the first, second and third lock parts, respectively, to limit the movement of the floating unit. A mechanism for limiting the vertical movement of the floating unit is provided in at least one of combinations of the first, second and third lock parts with the first, second and third engaging parts.