A cooling device for an internal combustion engine includes a circulation path, a coolant temperature sensor, a coolant pump, and an electronic control unit. The electronic control unit is configured to execute processing for performing feedback control on power of the coolant pump such that the output of the coolant temperature sensor becomes a target temperature, micelle determination processing for determining whether or not micelles are added to a coolant based on pump work of the coolant pump and the flow rate of the coolant flowing through the circulation path, Toms determination processing for determining whether or not the flow rate of the coolant satisfies a Toms effect expression condition, and correction processing for increasing a relative value of the output of the coolant temperature sensor with respect to the target temperature when the micelles is added and the Toms effect expression condition is established.