In order to correctly measure a temperature of a working fluid flowing through an outlet/inlet of a heat exchanger body, a flow adjustment ring is disposed within at least either one of a high-temperature inlet pipe and a low-temperature inlet pipe of the heat exchanger body. In this manner, a core region in which velocity and temperature of the working fluid becomes approximately constant is formed on a downstream side of the flow adjustment ring. A temperature sensor is provided in such a manner that a sensing point is arranged in this core region.