PURPOSE: To reduce a compression ratio whenever necessary, alleviate a load on a drive source and lessen the waste of consumption energy by reducing the take-in volume of a sealed space formed with a cylinder block and a piston through the change of connecting rod length.

CONSTITUTION: This invention applies to an oscillating type compressor for a car airconditioning device and the like. A connecting rod as connected to the piston 17 of the compressor according to this invention, comprises a rod 32 at the female side thereof and another rod 33 at the male side as coupled to said rod 32. For these rods 32 and 33, a stopper 36 and another stopper 34 are formed respectively at the male and female sides thereof, and a coil spring 35 is positioned between said stoppers 34 and 36. And the constitution is so made that the length of the connecting rod can be adjusted by the change of a differential pressure between a crank chamber 1a and a suction chamber 9 die to the opening and closing of a solenoid valve 31 and by the function of the coil spring 35.