To improve both performance of acceleration and a feeling of cooling, by detecting an acceleration condition of an engine for a vehicle, and changing a delivery capacity from a large capacity to a small capacity.

A booster passage 55 connecting a delivery chamber 39 and a crank chamber 15 is provided in a cylinder block 12, an opening/closing valve V is arranged in the passage 55. This opening/closing valve V is constituted so as to open the passage 55 by centrifugal force when a drive shaft 16 is rotated. When the opening/closing valve V is opened in an acceleration condition of a compressor, a pressure in the crank chamber 15 is increased, a tilt angle of a swash plate 21 is decreased, the compressor is switched from large capacity operation to small capacity operation so that acceleration performance is improved. The swash plate 21 is switched from a 100% large capacity to a 50% capacity, an excessive lowering of a cooling capacity is prevented.