According to the present invention, in a heating apparatus (1) having a viscous heater (9) using viscous fluid for heating cooling water, when an engine rotational speed is lower than a set rotational speed relative to a temperature of viscous fluid, a viscous clutch (7) is turned on to transmit a rotational driving force of the engine to a rotor (53) of the viscous heater. In this way, a shearing force is applied to the viscous fluid in the heat-generating chamber (50), and the circulating cooling water is heated by generated heat of the viscous fluid to improve the heating capacity. When the engine rotational speed is higher than the set rotational speed relative to a temperature of viscous fluid, the viscous clutch is not turned on. Therefore, the rotational driving force of the engine is not transmitted to the rotor of the viscous heater, so that the shearing force is not applied to the viscous fluid to prevent the oil temperature of the viscous fluid from increasing excessively higher than 200 °C.