A rotary compressor is comprised of a first housing having an intake chamber for receiving therein a fluid of variable pressure, and a second housing having an inner peripheral surface to define a working chamber and an inlet communicating between the working and intake chambers. A rotor is rotatably mounted in the working chamber and has a vane slidably supported in the rotor to maintain contact with the inner peripheral surface of the second housing during the rotation of the rotor to thereby compress the fluid flowing into the working chamber through the inlet. A rotary valve is rotatably disposed between the intake chamber and working chamber for regulating the flow rate of the fluid flowing through the inlet in response to angular displacement of the rotary valve. A piston is slidably disposed in a cylinder provided in the first housing. The piston has a front end exposed to the fluid in the intake chamber through one opening of the cylinder and a rear end exposed to the outside through the other opening of the cylinder so that the piston undergoes linear displacement in the cylinder in response to the variable fluid pressure applied to the front end of the piston. The linear movement of the piston is converted by a mechanical link into the angular displacement of the rotary valve.