A refrigeration cycle apparatus (50) includes: a main refrigerant circuit (21) having a compressor (1), a radiator (2), a first expansion mechanism (5), a second expansion mechanism (6), and an evaporator (4); an injection passage (22) for supplying an intermediate-pressure refrigerant to an injection port 1c of the compressor 1; and a water circuit (30) through which water to be heated in the radiator (2) flows. The refrigeration cycle apparatus (50) includes a sub heat exchanger (3) for cooling the water in the water circuit (30) by exchanging heat between the refrigerant in the injection passage (22) and the water to be heated in the radiator (2).