A control device performs deterioration diagnosis of a gas sensor including a pump cell and a sensor cell. The control device includes a control unit, a determination value acquisition unit, a diagnosis unit, and a correction unit. The control unit temporarily reduces the oxygen removal capability of the pump cell. The determination value acquisition unit acquires an output ratio of the sensor cell based on an output value of the sensor cell in a state where the oxygen removal capability of the pump cell is temporarily reduced. The diagnosis unit performs deterioration diagnosis of the gas sensor by comparing the output ratio with a determination threshold. The correction unit sets a correction coefficient based on an atmospheric pressure and an oxygen concentration, and also corrects the output ratio using the correction coefficient.