To provide a duct mounting structure for allowing easy mounting of a duct on an interior member for a cabin without lowering mechanical strength by utilizing a passing hole left after pulling a blowing pin as a part of a mounting means after performing blow molding.

The duct 20 is undetachably mounted by locating the passing hole 40b left when performing blow molding of the duct 20 at a portion adjacent to opening parts 26 of a duct side part 20a so that the dimension of one opening part 26 of the duct 20 may be fitted into an outlet 12a to be an air blow-off port, protruding a pin 14 at a portion corresponding to the passing hole 40b in the outlet 12a and fitting the pin 14 into the passing hole 40b.