PURPOSE: To simplify construction of a compressor entirely and also to improve a volumetric efficiency by employing a hydraulic mechanism instead of a link work.

CONSTITUTION: From turning a rotary shaft 8 a fourth clockwise with a driving gear (not illustrated), an eccentric shaft 9 turns slidably at the center of a slider 10 to descend and a hydraulic piston body 14 moves rightwards. A liquid in the right hydraulic cylinder 16 enters the right liquid chamber 27 in a hydraulic oscillating cylinder 22 through the right branch passage 20, and a hydraulic oscillating vane 25 gets turning clockwise. Since a liquid oscillating shaft 24 and a gas oscillating shaft 35 of a compressor 4 are linked through an oscillating shaft 7, the gas oscillating shaft 35 joins in oscillation with the liquid oscillating shaft 24. Then, a gas in gas chambers 38, 39 of a gas oscillating cylinder 34 is compressed by a gas oscillating vane 37 and introduced from an inlet port 40 to a discharge port 46.