The present invention provides a cooling device for an internal combustion engine of a vehicle. While the vehicle is in a decelerating state and while the internal combustion engine is in an idle reduction state, the cooling device increases the ratio of the cooling water circulation rate through a first path which extends through a heater core and a radiator while reducing the ratio of the cooling water circulation rate through a second path which bypasses the heater core and radiator. In addition, the cooling device increases the discharge flow rate of the electric water pump while the vehicle is in a decelerating state, and maintains the electric water pump in an operating state during idle reduction. Thus, the present invention allows accelerating the temperature decrease of the cylinder head during idle reduction, as well as improving fuel economy during acceleration when the vehicle is started.