There is disclosed a supercharger for an engine in which intake air is increased in pressure by the use of exhaust gas flowed into the supercharger from the engine, and is fed to the engine. An impeller 2, having a plurality of blades formed on an outer peripheral portion thereof, is received within a casing 1, and a ring-like fluid passage is formed around the plurality of blades, and a first partition 3 and a second partition 4 are provided in the fluid passage to divide this fluid passage into two fluid passages, that is, an exhaust gas passage 6 and an intake air passage 9. There is provided a fluid machine construction for causing the exhaust gas of the engine to flow into and out of the exhaust gas passage, and for causing the intake air to flow into and out of the intake air passage. With this construction, the pressure of the intake air can be satisfactorily increased over a wide range of the engine speed from a low speed to a relatively high speed, and therefore the supercharging of the engine can be effected with the inexpensive machine construction.