To provide a duct structure in a vehicular air conditioner capable of simplifying a layout in an instrument panel, reducing cost, reducing weight, and preventing the fogging of a side window by sharing an intermediate route with a side vent duct.

A duct 4a for a side window having a blowout port 4a opened toward a triangular window is branched from the vicinity of the blowout port 3a of the side vent duct 3 supplying cold air from an air conditioning unit toward an interior, and a duct outside air suction opening 43 is formed in the middle of the duct 4 for the side window.