A heat source-side unit comprising: a compression element; a liquid pipe; a heat source-side expansion valve connected to the liquid pipe; and a heat source-side heat exchanger, the heat source-side unit being connectable to a utilization-side unit including a utilization-side heat exchanger and a utilization-side expansion valve to constitute, in conjunction with the utilization-side unit, a refrigerant circuit configured to perform a refrigeration cycle in which the heat source-side heat exchanger functions as a radiator and the utilization-side heat exchanger functions as an evaporator, the heat source-side unit further comprising: a control unit configured to control the heat source-side unit to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger in the refrigeration cycle, wherein the oil recovery operation includes a first operation of decreasing an opening degree of the heat source-side expansion valve, and a second operation of increasing the opening degree of the heat source-side expansion valve, after the first operation, characterized in that the control unit performs the second operation when a first condition is established in the first operation, and in that the first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve on the liquid pipe and a pressure of the refrigerant sucked in the compression element has a value less than a predetermined value. a compression element; a liquid pipe; a heat source-side expansion valve connected to the liquid pipe; and a heat source-side heat exchanger, the heat source-side unit being connectable to a utilization-side unit including a utilization-side heat exchanger and a utilization-side expansion valve to constitute, in conjunction with the utilization-side unit, a refrigerant circuit configured to perform a refrigeration cycle in which the heat source-side heat exchanger functions as a radiator and the utilization-side heat exchanger functions as an evaporator, the heat source-side unit further comprising: a control unit configured to control the heat source-side unit to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger in the refrigeration cycle, wherein the oil recovery operation includes a first operation of decreasing an opening degree of the heat source-side expansion valve, and a second operation of increasing the opening degree of the heat source-side expansion valve, after the first operation, characterized in that the control unit performs the second operation when a first condition is established in the first operation, and in that the first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve on the liquid pipe and a pressure of the refrigerant sucked in the compression element has a value less than a predetermined value. a control unit configured to control the heat source-side unit to carry out an oil recovery operation of recovering an oil from the utilization-side heat exchanger in the refrigeration cycle, wherein the oil recovery operation includes a first operation of decreasing an opening degree of the heat source-side expansion valve, and a second operation of increasing the opening degree of the heat source-side expansion valve, after the first operation, characterized in that a first operation of decreasing an opening degree of the heat source-side expansion valve, and a second operation of increasing the opening degree of the heat source-side expansion valve, after the first operation, characterized in that the control unit performs the second operation when a first condition is established in the first operation, and in that the first condition includes at least a condition that a difference ΔP between a pressure of a refrigerant downstream of the heat source-side expansion valve on the liquid pipe and a pressure of the refrigerant sucked in the compression element has a value less than a predetermined value.