The present invention is a regulating device configured to regulate a temperature T2 of a first medium in accordance with a target temperature. The regulating device comprises a heat exchanger 16, a control valve 14, temperature sensors 2 and 4, temperature sensors 6 and 8, and a heat quantity control unit 30 and a temperature control unit 50 configured to calculate a target exchange heat quantity in the heat exchanger 16, calculate an exchange heat quantity in the heat exchanger 16, add a signal dependent upon a difference between the target exchange heat quantity and the exchange heat quantity to a signal dependent upon a difference between an output of the temperature sensor 4 and the target temperature, and control the control valve 14 so that a difference between the output of the temperature sensor 4 and the target temperature is reduced.