Motor bodies are housed between a case and a case-inner, with the whole of the outside-periphery surrounded by an outer peripheral wall. The upper-side-outer-peripheral face of the outer-peripheral wall slopes continuously downwards on progression from an uppermost portion of the outer-peripheral face towards a vehicle right side edge of the outer-peripheral face, and slopes continuously downwards from the uppermost portion towards the vehicle left side edge of the outer-peripheral face. Accordingly, even suppose water is to reach the upper side of the upper-side-outer-peripheral face, the upper-side-outer peripheral face of the outer-peripheral wall causes such water to always flow downwards towards the lower side of the outer-peripheral wall, and hence water can be suppressed or prevented from remaining standing on the upper-side-outer peripheral face of the outer-peripheral wall 46, enabling water to be suppressed or prevented from seeping in to the motor bodies.