PURPOSE: To avoid the operation stop of an air conditioner caused by the abnormal rise on the high pressure side of a refrigerating cycle by preventing the decrease of the wind quantity of outdoor blowers with the proper structure of vent holes against the action of the travel wind generated by the travel of a vehicle.

CONSTITUTION: A straight duct opened on the lower face at both ends is provided in the longitudinal direction under the floor of a vehicle, an outdoor heat exchanger 2 is arranged in it, outdoor blowers 3, 4 are arranged in series in opposite blowing directions at the front and rear of the heat exchanger 2, the outdoor blower 3 located on the top vehicle side is operated in the forward direction, and the outdoor blower 4 located on the tail vehicle side is operated in the reverse direction.