PURPOSE: To discriminate whether an auxiliary battery is rightly set or not by detecting the voltage of the auxiliary battery set to a facsimile equipment by an A/D converter.

CONSTITUTION: When an auxiliary battery 13 is rightly set to a facsimile equipment 1, the voltage V 1 of the auxiliary battery 13 is converted into prescribed voltage V 2 by a regulator 14. An A/D converter 15 detects this voltage V 2 and transmits the corresponded digital signal to a CPU 2. The CPU 2 receives this digital signal and discriminates that the auxiliary battery 13 is rightly set. When the terminal of the auxiliary battery 13 is inversely set, the voltage applied on the input side and the output side of the regulator 14 becomes Ov. The A/D converter 15 detects this voltage of Ov and transmits the corresponded digital signal to the CPU 2. The CPU 2 receives this digital signal, discriminates that the terminal of the auxiliary battery 13 is inversely set and displays the effect on a display part 6.