A control device for controlling an oxygen concentration sensor includes: a voltage sweeping unit for applying a voltage to the sensor for a time interval during an impedance detection process; a pre-sweeping voltage memory for storing a terminal voltage of the sensor as an initial terminal voltage just before applying the voltage; an impedance detection unit for detecting an element impedance; a voltage returning unit for returning the terminal voltage to the initial terminal voltage after a predetermined time interval has elapsed; a monitoring unit for monitoring the terminal voltage after the voltage returning unit starts returning the terminal voltage; a determination unit for determining whether a monitored terminal voltage of the sensor reaches a stored terminal voltage in the memory; and a stop unit for stopping a returning operation of the voltage returning unit when the monitored terminal voltage reaches the stored terminal voltage.