A rotary valve operationally connected to a rotary shaft is housed so as to be slidably rotatable in an accommodation hole formed in a cylinder block. A suction valve mechanism functions so as to introduce refrigerant gas in a suction chamber into a compression chamber. A gas suction passage leading from the suction chamber to the compression chamber can be opened and closed in synchronism with rotation of the rotary shaft. In an outer circumferential surface of the rotary valve is formed a groove constituting a part of a gas vent passage for introducing the refrigerant gas in a crank chamber into the compression chamber. <IMAGE>
