A front upper support surface and a rear upper support surface facing an upper surface of a rear end of an operation handle are provided in a lock release lever with a gap between the front upper support surface and the rear upper support surface in the vehicle front-rear direction, and front lower support surfaces are provided below the front upper support surface. An upper rail is provided with a rear lower support surface, which is positioned below a rear upper support surface. A clearance is provided between the front lower support surface and a lower surface of a rear end of the operation handle, and a clearance is provided between the rear lower support surface and the lower surface of the rear end of the operation handle.