The present invention is intended to provide a technique which makes effective use of a phase transition temperature zone of cooling water by controlling a control valve for changing the temperature of the cooling water in an appropriate manner. The present invention resides in a cooling water temperature control apparatus for an internal combustion engine in which cooling water is caused to circulate, said cooling water having variable specific heat, said apparatus comprising: a received heat amount calculation unit configured to calculate an amount of received heat which is received by said cooling water, a control valve that is controlled to open and close according to a command so as to change a circulation route or an amount of circulation of said cooling water and to change the temperature of said cooling water, and a control unit configured to control said control valve based on the amount of received heat which is calculated by said received heat amount calculation unit.