PURPOSE: To make a discharge rate variable as well as to aim at the improvement of operatbility and economization in power consumption, by installing a holding device which engages and holds a vane in a position drawing it into a slit at a shifting section in the vane rotative direction from the suction start position to the discharge completion position of a compression chamber.

CONSTITUTION: At a shifting section in the rotative direction of a vane 1 from the suction start position to the discharge completion position, a notch part 7a of each vane 7 comes into a state of being engaged with a holder 20, while each of these vanes 7 is held in a state of being embedded into a slit 6a whereby compressive operation in a compression chamber 9 will not take place. When each vane 7 runs past an end part of the holder 20 after passing through a discharge hole 9b, the notch part 7a comes off the holder 20, while inside a compression chamer 10, each vane 7 is forcibly pressed against a cam peripheral surface 2a and performs compressive operation. That is, each vane 7 performs the compressive operation for only at a half-round interval for the duration of one rotation of a rotor 6 so that compressor capacity is reduced to half. With a discharge rate made variable like this, in time of low cooling load, on-off frequency after being compressed by a thermostat can be reduced.