A cooling device for an internal combustion engine, the cooling device comprising: a circulation path for a coolant, the circulation path including a water jacket of the internal combustion engine; a coolant temperature sensor disposed on the circulation path, the coolant temperature sensor being configured to detect a coolant temperature; a coolant pump disposed on the circulation path; and an electronic control unit configured to control the coolant pump based on an output of the coolant temperature sensor, wherein 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 the coolant based on pump work of the coolant pump and a flow rate of the coolant flowing through the circulation path, Toms determination processing for determining whether or not the flow rate 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. a circulation path for a coolant, the circulation path including a water jacket of the internal combustion engine; a coolant temperature sensor disposed on the circulation path, the coolant temperature sensor being configured to detect a coolant temperature; a coolant pump disposed on the circulation path; and an electronic control unit configured to control the coolant pump based on an output of the coolant temperature sensor, wherein 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 the coolant based on pump work of the coolant pump and a flow rate of the coolant flowing through the circulation path, Toms determination processing for determining whether or not the flow rate 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. 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 the coolant based on pump work of the coolant pump and a flow rate of the coolant flowing through the circulation path, Toms determination processing for determining whether or not the flow rate 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.