A ventilating device for ventilating a vehicle includes a frame defining an opening and a closing device including at least one closing flap extending in a general direction in the opening. The closing device is movable between open and closed positions such that a passage surface for the air through the ventilating device is smaller than the passage surface for the air when the closing device is in the open position. The flap is movable between open and closed positions and is mounted pivotably on the frame in order to pivot between the open and closed positions. The closing device includes a guide system for guiding the flap, which is arranged between two ends of the flap and includes a guide slot and a pin moving in the guide slot between the open and closed positions.