A refrigerant cycle device includes a compressor driven by a vehicle engine for drawing and compressing gas refrigerant from an evaporator, a variable displacement mechanism which varies a discharge capacity of the compressor based on a control value from an exterior to approach a suction pressure of the compressor to a predetermined suction pressure, and a control unit for controlling the discharge capacity of the compressor. The control unit includes a determining part for determining an accelerating state of the vehicle engine, a detecting member which detects a thermal load of the evaporator, a setting part for setting a minimum control value in accordance with the thermal load, and a controlling part. The controlling part reduces the control value to the minimum control value and returns the reduced control value to a control value before the reducing, when the determining means determines an accelerating state of the vehicle engine.