PURPOSE: To prevent a mistake of an operating condition by nullifying an operating condition of a nonvolatile memory, when an electric power source is not recovered even when a prescribed time has elapsed, after an electric conduction to a machine device having the nonvolatile memory is cut off.

CONSTITUTION: A CPU1 displays 5 information through an I/O device 4 to an RAM3 backed up by a battery in accordance with a data (for instance, the number of copy sheets of a copying machine, a copying magnification, a density, etc.) set by a user, by a program stored in an ROM2. Subsequently, copying is executed by driving a charging relay 6 for a transfer charger and a separating charger. When a service interruption occurs in the course of copying, a timer 7 is started, and if the service interruption continues longer than the time set in advance, a data in the RAM3 is nullified by an output of the timer. In this way, it is possible to prevent an error of an operating condition at the time of reuse after a service interruption of many hours.