Recently, use of superchargers has been popularized as a means of improving output of passenger car engines. Supercharging is not a new problem. Gottlieb Daimler published an idea to supercharge a gasoline engine by a mechanically driven superchager in 1885 in DRP 34926 (Ref. 1)*. Two types of supercharging are used currently; turbo supercharging and mechanical supercharging. Turbo superchargers (exhaust gas turbine superchargers) are used in most case, however, have a weak point that the supercharging effect at a low speed is very small. For low speed operation, mechanical superchargers which can improve, this weak point greatly, are rather preferable to be used. However, they have several disadvantages, such as, with an increase in speed, power loss increases, delivery air temperature rises, delivery air density lowers, and so on. For automotive engine superchargers, it is necessary to overcome these problems.