To dispense with a wiring for connection to an on-board battery by fitting a solar cell to demonstrate a function as a forward light quantity detection sensor, is directed to a forward side of a vehicle, and is capable of charging a secondary battery to a housing.

A solar cell 11 to generate the power by the light on the forward side is fitted to a housing on a forward side along the longitudinal direction so as to perform the function as a forward light quantity detection sensor to detect the light quantity on the forward side along the longitudinal direction of a vehicle. In fitting the solar cell 11, the solar cell 11 is preferably embedded in the synthetic resin housing so as to be flush with the surface as the housing, or the solar cell 11 is preferably attached to the housing. The voltage applied to an electro-chromic layer 4 built in a mirror is controlled by a drive and control means 12. A secondary battery 13 to supply the power to the drive and control means 12 and the drive and control means 12 are stored in the housing.