In an apparatus for heating an intake system for an engine of a vehicle by hot water, the vehicle having an engine compartment placed in a front part, in which a radiator is placed on a front side, and the engine and the intake system are placed behind the radiator. The intake system includes an intake passage and a throttle device. A hot water passage is provided to circulate hot water around the throttle device to heat the throttle device, the hot water having been warmed by cooling the engine. In the hot water passage, a hot water control valve is provided. In the hot water control valve, an expanding-contracting member made of shape-memory alloy is provided to control opening and closing of the hot water control valve in response to the internal temperature of the engine compartment.