Abstract: Disclosed herein is a rotary pump in which one or more rotors including rotary cylinders and rotary pistons rotate upon inside a housing having a suction hole and a discharge hole to compress a pump fluid. More particularly, the two rotary pistons are arrange to revolve about a rotating shaft in a state wherein the center of mass of the two rotary pistons coincide with that of the rotating shaft, thereby achieving not only a reduction in the generation of vibrations or noise, but also a variation in the flow of rate of fluid. The rotary pump may have a cover, which is opened or closed in accordance with a pressure, to prevent the generation of backflow and pulsations in accordance with the rotation of the rotary pump when the pressure of the discharge hole differs from that of the suction hole.