A heat source-side unit to be connected to a utilization-side device to constitute a refrigerant circuit in conjunction with the utilization-side device, the heat source-side unit comprising: a heat source-side circuit constituting at least a part of the refrigerant circuit ; and a control unit configured to control an operation of the heat source-side circuit , wherein the heat source-side circuit includes: a compression unit including a lower-stage compression element configured to compress a refrigerant, and a higher-stage compression element configured to further compress the refrigerant compressed by the lower-stage compression element ; an intermediate heat exchanger disposed on a refrigerant path between the lower-stage compression element and the higher-stage compression element and configured to cause the refrigerant to exchange heat with a heating medium; and a bypass passage connected to a suction pipe and a discharge pipe each connected to the lower-stage compression element , for bypassing the lower-stage compression element , characterized in that the control unit is configured to perform a first action of stopping the lower-stage compression element and operating the higher-stage compression element at startup of the compression unit , and the control unit is configured to perform the first action on condition that a suction pressure of the compression unit has a value more than a predetermined value. a heat source-side circuit constituting at least a part of the refrigerant circuit ; and a control unit configured to control an operation of the heat source-side circuit , wherein the heat source-side circuit includes: a compression unit including a lower-stage compression element configured to compress a refrigerant, and a higher-stage compression element configured to further compress the refrigerant compressed by the lower-stage compression element ; an intermediate heat exchanger disposed on a refrigerant path between the lower-stage compression element and the higher-stage compression element and configured to cause the refrigerant to exchange heat with a heating medium; and a bypass passage connected to a suction pipe and a discharge pipe each connected to the lower-stage compression element , for bypassing the lower-stage compression element , characterized in that a compression unit including a lower-stage compression element configured to compress a refrigerant, and a higher-stage compression element configured to further compress the refrigerant compressed by the lower-stage compression element ; a lower-stage compression element configured to compress a refrigerant, and a higher-stage compression element configured to further compress the refrigerant compressed by the lower-stage compression element ; an intermediate heat exchanger disposed on a refrigerant path between the lower-stage compression element and the higher-stage compression element and configured to cause the refrigerant to exchange heat with a heating medium; and a bypass passage connected to a suction pipe and a discharge pipe each connected to the lower-stage compression element , for bypassing the lower-stage compression element , characterized in that the control unit is configured to perform a first action of stopping the lower-stage compression element and operating the higher-stage compression element at startup of the compression unit , and the control unit is configured to perform the first action on condition that a suction pressure of the compression unit has a value more than a predetermined value. <EOS>