A refrigeration cycle apparatus comprising a refrigerant circuit, the refrigerant circuit comprising a compressor, a load-side heat exchanger, an expander, a heat source-side heat exchanger, a first four-way valve, and a second four-way valve, which are connected by pipes so that refrigerant is circulated through the refrigerant circuit, the expander comprising: an expander shell defining an outer shell of the expander and storing refrigerant machine oil; an expansion unit arranged in the expander shell, the expansion unit being configured to expand the refrigerant flowing out from the load-side heat exchanger or the heat source-side heat exchanger that serves as a condenser to generate driving force, and configured for causing the expanded refrigerant to flow into the load-side heat exchanger or the heat source-side heat exchanger that serves as an evaporator, a power generator arranged in the expander shell, the power generator being configured to rotate by the driving force generated by the expansion unit; and a rotation shaft coupling the power generator to the expansion unit, the expander shell including: an inlet configured for allowing the refrigerant to flow into the expander shell; and an outlet configured for allowing the refrigerant that flowed into the expander shell from the inlet to flow out from the expander shell and to flow into a suction-side pipe of the compressor, the expander shell being configured such that the refrigerating machine oil contained in the refrigerant is stored therein, and is supplied to at least one of the expansion unit and the power generator, the expansion unit including: an expansion unit inlet configured for allowing the refrigerant to flow into the expansion unit from an inlet pipe; and an expansion unit outlet configured for allowing the refrigerant flow out from the expansion unit and to flow into an outlet pipe, the inlet pipe being connected to the condenser (2, 4) through the second four-way valve, the outlet pipe being connected to the evaporator (2, 4) through the second four-way valve, characterized in that the refrigeration cycle apparatus further comprises; a second bypass pipe configured to branch off from a passage from the condenser (2, 4) to the expansion unit, to decompress the refrigerant and to cause the refrigerant to flow into the inlet of the expander shell; and a heat exchanger configured to exchange heat between the refrigerant branched off and decompressed at the second bypass pipe and the refrigerant flowing from the condenser (2, 4) into the expansion unit. an expander shell defining an outer shell of the expander and storing refrigerant machine oil; an expansion unit arranged in the expander shell, the expansion unit being configured to expand the refrigerant flowing out from the load-side heat exchanger or the heat source-side heat exchanger that serves as a condenser to generate driving force, and configured for causing the expanded refrigerant to flow into the load-side heat exchanger or the heat source-side heat exchanger that serves as an evaporator, a power generator arranged in the expander shell, the power generator being configured to rotate by the driving force generated by the expansion unit; and a rotation shaft coupling the power generator to the expansion unit, an inlet configured for allowing the refrigerant to flow into the expander shell; and an outlet configured for allowing the refrigerant that flowed into the expander shell from the inlet to flow out from the expander shell and to flow into a suction-side pipe of the compressor, an expansion unit inlet configured for allowing the refrigerant to flow into the expansion unit from an inlet pipe; and an expansion unit outlet configured for allowing the refrigerant flow out from the expansion unit and to flow into an outlet pipe, a second bypass pipe configured to branch off from a passage from the condenser (2, 4) to the expansion unit, to decompress the refrigerant and to cause the refrigerant to flow into the inlet of the expander shell; and a heat exchanger configured to exchange heat between the refrigerant branched off and decompressed at the second bypass pipe and the refrigerant flowing from the condenser (2, 4) into the expansion unit.