PURPOSE: To control an airflow, by a method wherein an electromagnet engages a magnetic rod in a solenoidal manner which is mounted on at least either valve members of a suction valve and a discharge valve, which a current, synchronizing with the rotation of a compressor, is caused to flow to the electromagnet, whereby the closing delay time of the suction valve or discharge valve is regulated.

CONSTITUTION: A rod 6, connected to a suction valve 4, consists of a permanent magnet, and the rod 6 magnetically engages an electromagnet 8 placed in a suction chamber 7. The electromagnet 8 is connected to a controller 9 located outside. A signal S from a detector (not shown) at a rotation angle of a crank shaft, is inputted to the controller 9, is detected, and a direct current is caused to flow to the electromagnet 8 for a time T. During said energization, the suction valve 4 does not close. The time T for which the direct current is applied, can be adjusted within a time period corresponding to the rotation angle of the crank shaft ranging from 180°-360°. In a compressor body, the above function permits a continuous control of capacity within a range from 0W100% corresponding to load.