There is provided an air pump in which vibration noise generated in a drive unit of the pump is suppressed from being transmitted to the outside through a suction passage. A casing of the air pump has a suction port extending from an outer peripheral surface to inner peripheral surface of the casing, a noise reduction wall annularly formed on the outer peripheral surface of the casing such that the suction port opens in a region of the outer peripheral surface of the casing surrounded by the noise reduction wall, and a lid member closing the opening of the top of the noise reduction wall and cooperating with the noise reduction wall and the outer peripheral surface of the casing to define a noise reduction chamber communicating with the suction port. The noise reduction wall has an elongated noise reduction passage extending circumferentially in the noise reduction wall.