In a refrigeration cycle apparatus having an expansion mechanism, a method to swiftly generate a pressure difference upstream and downstream of the expansion mechanism of, thereby enhancing the starting performance of the refrigeration cycle apparatus The apparatus has a compression mechanism, a utilizing-side heat exchange, an expansion mechanism for recovering power, and a heat source-side heat exchanger. The revolution number of the heat source fluid transfer means is made smaller than a target revolution number or the heat source fluid transfer means is stopped during a predetermined time after the compression mechanism is started. When the compression mechanism is started, the pressure difference can be generated upstream and downstream of the expansion mechanism for a short time, the operation of the expansion mechanism does not become unstable, vibration and noise can be prevented, and the refrigeration cycle apparatus can swiftly be started.