PURPOSE: To simplify the structure by eliminating flexibility, and to avoid the enlargement of the whole of a device.

CONSTITUTION: In the case of forming a supercharger for motorcycle, which is loaded with a unit swing type engine 15 formed by unifying an engine unit 17 and a rear wheel transmitting device 18, a connecting rod supercharging mechanism 33a, which compresses the intake air with the oscillation of a connecting rod 25, is provided in a crank case 21. An air cleaner 35 for filtering the air to the supercharging mechanism 33a, an inter cooler 36 for cooling the pressurized air from the supercharging mechanism, and a supercharging tank 37 for storing the pressurized air from the inter cooler 36 are installed in the unit swing type engine unit 15 so as to be oscillated with the engine unit.