A gas sensor processing apparatus (1) which includes voltage shift means (11, 19, S1071) for shifting a detection element voltage VE produced between electrodes (3P, 3N) of a detection element (3) from a pre-shift voltage VE1 to a post-shift voltage VE2; recovery means (11, 19, S1072) for returning the detection element voltage VE from the post-shift voltage VE2 to the pre-shift voltage VE1 after the end of a voltage shift period TS in which the voltage VE is shifted by the voltage shift means; and deterioration index detection means S106-S107 for detecting a deterioration index ID representing the degree of deterioration of the detection element (3) on the basis of a voltage change in the recovery period TK in which the voltage VE is recovered by the recovery means.