PURPOSE: To provide an outside air introduction device of an automobile capable of avoiding dust accumulated in the neighbourhood of an outside air intake port from being sent into a car room with outside air at the time of starting working of a fan.

CONSTITUTION: Outside air sent out from a fan 15 is introduced to an outside air intake port 11 through an outside air returning duct 31 and dust accumulated there is blown off before outside air sucked from the outside air intake port 11 begins to be sent to car interior 3 by working of the fan 15.