PURPOSE: To freely control the ventilation for a vehicle by providing a shield plate for selecting the introduction or exhaust of air at the inside of a vehicle of a mounting unit having an atmospheric air introduction side front chamber and an exhaust gas side rear chamber.

CONSTITUTION: When a shield plate 9 is shifted to an air introduction side by a handle 10, pressure air received on the front surface of a door mirror unit 4 according to the vehicle speed is introduced from a vent hole 4e into a front chamber 4c through a vent hole 5e of a mounting unit 5 into an automotive compartment with fresh air. When the plate 9 is shifted to the exhaust side, contaminated air in the compartment is exhausted from the vent hole 5e through exits 4f formed in a plurality. When the plate 9 is disposed at the neutral position, passages P, P1 are together closed, and the quality of air to be introduced can be readily controlled by the rotary amount.