PROBLEM TO BE SOLVED: To provide a cooling water temperature control system capable of increasing temperature of cooling water of an engine to a proper temperature without wastefully consuming a fuel.SOLUTION: A target increase amount of a cooling water temperature per unit time is determined, and it is determined whether or not control for increasing a heating value of an engine is necessary depending on whether an actual increase amount of the cooling water temperature is smaller than the target increase amount or not. Therefore, even when the temperature of the cooling water of an engine is lower than the target cooling water temperature, if the actual increase amount of the cooling water temperature surpasses the target increase amount, the control for increasing the heating value of the engine is not executed. This is because, in this case, it can be determined that a necessary heating value can be acquired by an operation of the engine for allowing a vehicle to travel. As a result, excessive fuel consum
