A visibility adjusting section (10) is formed by making a visible light transmission of a region (A) in a lower side of left and right ridgelines (Rl, Rr) lower than a visible light transmission of a region (B) in an upper side of the left and right ridgelines (Rl, Rr). Accordingly, a driver and a passenger on an assistant driver's seat can see an outer side of a vehicle through the visibility adjusting section (10), and a suitable light can be taken into the vehicle. Further, since a parting line (11) of the visibility adjusting section (10) is uniformly inclined downward toward opposite sides in a vehicle-width direction from an apex (T) disposed at a position which is deviated from a driver, a driving posture of the driver is stabilized, and it is possible to suppress a disturbance in a steering operation.