An air pump is disclosed, the lower end of a drive shaft is in active connection with an eccentric hole on an eccentric wheel, and vents are opened on a hole wall of the eccentric hole to use as a heat sink in such a way to expose the lower end of the drive shaft to the outside through the vents, thereby facilitating cooling. In addition, the lower end of the drive shaft is formed into a reduced diameter section corresponding to vents, the edges of which are positioned on the reduced diameter section so as to increase an avoidance clearance, avoiding the friction generated between burrs generated on the edge of the vent upon manufacturing and the drive shaft, thereby improving the product life.