A refrigeration cycle apparatus in which a refrigerant is circulated, comprising: a refrigeration cycle mechanism that has a compressor whose operating frequency can be controlled, a first radiator that supplies heat by means of the refrigerant to tank water that is water stored in a hot water storage tank, a first pressure-reducing mechanism, and a first evaporator, the refrigerant circulating in an order of the compressor, the first radiator, the first pressure-reducing mechanism, and the first evaporator; and a controller, wherein the controller includes, a memory section that stores control period information indicating a preset control period, and is capable of storing other information, a computing section that calculates a heat consumption on a time period basis, the heat consumption indicating a quantity of heat that has been supplied to an outside by the tank water within the time, the time period being one of divided predetermined time periods of a day, stores the calculated heat consumption and a corresponding point in time into the memory section, and computes current heat storage in the tank water, and a controlling section that controls the operating frequency of the compressor, wherein the computing section, from the heat consumptions of at least one day in the past stored in the memory section, calculates a maximum heat consumption that is to be the largest among other heat consumptions to be generated on a current day and a maximum consumption time that is a corresponding point in time to the maximum heat consumption, at a time that precedes the maximum consumption time by the control period, computes the heat storage in the tank water, and on a basis of the heat storage and the maximum heat consumption of the current day, computes a hot water supply capacity target and the operating frequency of the compressor, the hot water supply capacity target serving as a heat rejection target value necessary for the first radiator to bring the heat storage in the tank water into the maximum heat consumption at the maximum consumption time, wherein the controlling section controls the compressor at the operating frequency computed by the computing section, and wherein the computing section updates the control period stored in the memory section on a basis of the hot water supply capacity target, and uses the updated control period for computing the operating frequency of the compressor in accordance with the maximum heat consumption on a following day. a refrigeration cycle mechanism that has a compressor whose operating frequency can be controlled, a first radiator that supplies heat by means of the refrigerant to tank water that is water stored in a hot water storage tank, a first pressure-reducing mechanism, and a first evaporator, the refrigerant circulating in an order of the compressor, the first radiator, the first pressure-reducing mechanism, and the first evaporator; and a controller, wherein the controller includes, a memory section that stores control period information indicating a preset control period, and is capable of storing other information, a computing section that calculates a heat consumption on a time period basis, the heat consumption indicating a quantity of heat that has been supplied to an outside by the tank water within the time, the time period being one of divided predetermined time periods of a day, stores the calculated heat consumption and a corresponding point in time into the memory section, and computes current heat storage in the tank water, and a controlling section that controls the operating frequency of the compressor, a memory section that stores control period information indicating a preset control period, and is capable of storing other information, a computing section that calculates a heat consumption on a time period basis, the heat consumption indicating a quantity of heat that has been supplied to an outside by the tank water within the time, the time period being one of divided predetermined time periods of a day, stores the calculated heat consumption and a corresponding point in time into the memory section, and computes current heat storage in the tank water, and a controlling section that controls the operating frequency of the compressor,