To provide a supercharger having the improved assembling ability of timing gears having a pump function.

A pump unit 10 having a gear pump function and constituting the timing gears 11 and 12 for simultaneously operating a pair of rotors 4 and 5 is assembled to a side of a supercharger easing 1 structured so as to discharge fluid sucked from a suction port by pump operation of the pair of rotors 4 and 5. A special lubricating oil pump unit is not required, the number of components, weight, and required space are reduced, a driving pulley is not required to improve engine efficiency, and the pump unit 10 constituting the timing gears 11 and 12 unitized by generalizing a body assembled with the rotors 4 and 5 as the supercharger can be independently easily mounted on a various supercharger. The timing gears 11 and 12 themselves are lubricated with oil to reduce gear noise.