For a purpose of realizing a refrigerant cycle apparatus capable of exactly detecting a pressure reverse phenomenon caused in a compression element of a compressor of a multistage compression type, in the refrigerant cycle apparatus in which the multistage compression type compressor constitutes a refrigerant circuit, including an electromotive element, and first and second compression elements driven by the electromotive element in an airtight container to suck an intermediate-pressure refrigerant gas compressed by the first compression element into the second compression element and to compress and discharge the refrigerant gas, the apparatus comprising: a sensor for detecting a discharge refrigerant pressure of the first compression element; and a control device into which an output of the sensor is input, the control device detects reverse of the discharge refrigerant pressures of the first and second compression elements based on the discharge refrigerant pressure of the first compression element.