A heat source unit constitutes part of a basic refrigerant circuit including: a compressor that compresses refrigerant; an accumulator that temporarily accumulates the refrigerant before the refrigerant is sucked into the compressor; an oil separator that separates refrigerating machine oil from the refrigerant after the refrigerant has been discharged from the compressor; a heat source-side heat exchanger that functions as a radiator or an evaporator of the refrigerant; a liquid refrigerant communication pipe; utilization-side expansion valves; utilization-side heat exchangers; and a gas refrigerant communication pipe that are connected to one another, the heat source unit comprising refrigerant circuit constituent parts including the compressor, the accumulator, the oil separator, and the heat source-side heat exchanger that are provided inside a casing, and the refrigerant circuit constituent parts being changed or added in accordance with capacity or function.