In a refrigeration cycle apparatus having an expansion mechanism, it is an object of the present invention to swiftly generate a pressure difference upstream and downstream of the expansion mechanism of , thereby enhancing the starting performance of the refrigeration cycle apparatus. In a control method of a refrigeration cycle apparatus comprising a compression mechanism 2, a utilizing-side heat exchanger 3, an expansion mechanism 5 for recovering power, a heat source-side heat exchanger 6, and heat source fluid transfer means 9 for transferring a heat source fluid to the heat source-side heat exchanger 6, revolution number of the heat source fluid transfer means 9 is made smaller than target revolution number or the heat source fluid transfer means 9 is stopped during a predetermined time after the compression mechanism 2 is started. With this method, when the compression mechanism 2 is started, the pressure difference can be generated upstream and downstream of the expansion mechanism 5 for a short time, the operation of the expansion mechanism 5 does not become unstable, vibration and noise can be prevented, and the refrigeration cycle apparatus can swiftly be started.