An evaporator which heats working fluid with high-temperature fluid to evaporate the working fluid includes: a working fluid channel which is arranged in a flow direction of the high temperature fluid and through which the working fluid flows; and a temperature sensor which is provided for the working fluid channel. A part of the working fluid channel is exposed to outside of a housing of the evaporator, and the temperature sensor is provided in the part of the working fluid channel exposed to the outside of the housing of the evaporator in a region other than an inlet of the working fluid channel into which the working fluid flows from the outside of the evaporator and other than an outlet of the working fluid channel through which the working fluid flows out of the evaporator. The output value of the temperature sensor is used to adjust the temperature of the working fluid in the evaporator.