An internal combustion engine control device applied to an internal combustion engine, the internal combustion engine control device comprising: an injector-temperature calculation unit that calculates an injector temperature based on a coil resistance value of an injector; an internal-combustion-engine temperature calculation unit that calculates a temperature of the internal combustion engine based on the injector temperature; and an operating-state control unit that controls an operating state of the internal combustion engine based on the temperature of the internal combustion engine, characterised in that the internal combustion engine control device further comprises an integration-time calculation unit that calculates a driving time of the injector and calculates a fuel-injection integration time obtained by integrating the driving time in a predetermined period, and the internal-combustion-engine temperature calculation unit calculates an injector cooling amount so as to gradually shift toward an injector cooling-amount target value, calculated based on a value obtained by dividing the fuel-injection integration time by the predetermined period, to reach the injector cooling-amount target value, and calculates the temperature of the internal combustion engine based on a corrected injector temperature obtained by correcting the injector temperature with the injector cooling amount, or calculates a value obtained by subtracting an ambient temperature of the internal combustion engine control device from a predetermined reference temperature as an offset amount, calculates a value obtained by subtracting the offset amount from the injector temperature as a buffer temperature, and calculates the temperature of the internal combustion engine by correcting a base temperature of the internal combustion engine, calculated on the basis of the buffer temperature, with the injector cooling amount. an injector-temperature calculation unit that calculates an injector temperature based on a coil resistance value of an injector; an internal-combustion-engine temperature calculation unit that calculates a temperature of the internal combustion engine based on the injector temperature; and an operating-state control unit that controls an operating state of the internal combustion engine based on the temperature of the internal combustion engine, characterised in that the internal combustion engine control device further comprises an integration-time calculation unit that calculates a driving time of the injector and calculates a fuel-injection integration time obtained by integrating the driving time in a predetermined period, and the internal-combustion-engine temperature calculation unit calculates an injector cooling amount so as to gradually shift toward an injector cooling-amount target value, calculated based on a value obtained by dividing the fuel-injection integration time by the predetermined period, to reach the injector cooling-amount target value, and calculates the temperature of the internal combustion engine based on a corrected injector temperature obtained by correcting the injector temperature with the injector cooling amount, or calculates a value obtained by subtracting an ambient temperature of the internal combustion engine control device from a predetermined reference temperature as an offset amount, calculates a value obtained by subtracting the offset amount from the injector temperature as a buffer temperature, and calculates the temperature of the internal combustion engine by correcting a base temperature of the internal combustion engine, calculated on the basis of the buffer temperature, with the injector cooling amount.