A controller normally supplies current the magnitude of which corresponds to a required cooling performance of a refrigeration circuit to a displacement control valve. As a result the compressor displacement is adjusted in accordance with the required cooling performance (usual displacement control). When a vehicle is quickly accelerated, the controller temporarily eliminates the current value to the control valve to minimize the compressor displacement (displacement limiting control). When the control is switched from the displacement limiting control to the usual In displacement control, the controller changes the current value from zero to a target value, which corresponds to the required cooling performance, taking a predetermined restoration time. For an initial period of the restoration period, the current value is set greater than a corresponding value on a direct proportional line, which represents a constant rate of change from zero to the target value. As a result, the control is smoothly and quickly switched from the displacement limiting control to the usual displacement control.