A deterioration signal generation device for an oxygen sensor having a power supply different than a power supply connected to an external device, including a connection unit for electrically connecting the ground lines of the respective power supplies; a first acquisition unit for electrically connecting to a first output line at a reference potential side and to a second output line at a sensor potential side of the oxygen sensor, to obtain first and second potentials, respectively; an operation unit that calculates a first differential value between the first and second potentials; a processing unit that performs an operation on the first differential value; a second acquisition unit that acquires a third potential of a first input line at a reference potential side of the external device; and an output unit that generates the deterioration signal by superposing the second differential value on the third potential.