A controller is configured to, based on a characteristic information of thermal output with respect to a temperature difference between a hot end and a cold end of a working chamber, changes at least one of a flow rate of a heating target fluid in a high temperature heat exchanger and a flow rate of a cooling target fluid in a low temperature heat exchanger. At least one of the flow rate of the heating target fluid in the high temperature heat exchanger and the flow rate of the cooling target fluid in the low temperature heat exchanger is adjusted such that the temperature difference between the hot and cold ends changes in a direction that increases thermal output.