A fluid or powdery product dispensing device comprises a dispensing outlet (10), an air ejector (20) comprising a piston (21) that slides in an air chamber (22) to generate an air flow when the device is actuated, and at least one reservoir (30) containing a unit dose of the product, the reservoir comprising an air inlet (31) with a product retaining member (40) and a product outlet (32) closed by a closing element (50), the device comprising a mechanical opening system (61, 62) for ejecting the closing element mechanically from its closing position, the piston of the air ejector cooperating, in the rest position, in a non-sealing manner with the air chamber in order to connect the air chamber to the atmosphere.