PROBLEM TO BE SOLVED: To achieve cost reduction while ensuring ventilation characteristic and sound insulating properties during door opening/closing operation or the like, because, in a freight vehicle or the like, a ventilation duct for ventilating between the inside and the outside of a vehicle cabin is provided, for example, on a rear surface of the cabin in order to smoothly perform opening/closing operation of a door, however, conventionally, the ventilation duct is made to directly communicate with the same space as a vent hole on the inside of the vehicle cabin, therefore, a sound insulation cover is required to prevent duct flapping noise during vehicle traveling or the like, in this respect, it causes high costs.SOLUTION: A space between an outer panel 10 and an inner panel 11 of a rear quarter panel 2 is partitioned by a reinforcement 12 into a section 13 on the outside of a vehicle cabin and a section 14 on the inside of the vehicle cabin. A ventilation duct 15 attached to the section 13 on the outside of the vehicle cabin is made to communicate with the inside of the vehicle cabin via an air outlet 12a provided in the reinforcement 12, thereby eliminating a conventional sound insulation cover and achieving cost reduction while ensuring the ventilation characteristics and the sound insulating properties.