Abstract: A rotary piston type fluid machine comprises one or more rotary piston type fluid machine units, each comprising a doughnut type ring-shaped cylinder with an annular slit being provided in the wall at the inward periphery lying in a plane containing the annular central line of the cylinder, a rotor rotatively supported by the cylinder with the peripheral portion being shiftably received within the slit, one or more rotary pistons secured to the peripheral surface of the rotor and adapted to be shifted within the cylinder, and one or more gate valves mounted to the cylinder so as to cross the cylinder and adapted to periodically protrude into the cylinder in synchronization with the movement of the rotary pistons. The rotary piston type fluid machine unit can be utilized as a compressor, an internal combustion engine, a pump, etc. by using it singly, or as a number of the units in combination.