A cooling medium circulating apparatus includes first and second flow paths configured to circulate a cooling medium, and a flow path switchover unit for connecting or disconnecting between the first and second flow paths. A method for controlling a cooling medium circulating apparatus includes detecting temperatures of the cooling medium flowing through the flow paths. The method further includes calculating a temperature difference between temperatures of the cooling medium flowing through the first and second flow paths. In the cooling medium circulating apparatus and method, a prescribed cycle is set, and connecting and disconnecting periods are set. The connecting and disconnecting periods are periods for connecting and disconnecting, respectively, between the flow paths in the prescribed cycle. The flow path switchover unit is controlled based on the connecting and disconnecting periods. The prescribed cycle becomes shorter as the temperature difference becomes larger.