PURPOSE: To prevent the destruction of the programs or data stored by discriminating whether or not the normal working can be maintained by a power supply before application of the power supply.

CONSTITUTION: When a power supply is applied, an input/output part 14 delivers the power ON signal directly to a power supply ON/OFF control means 5. Then a control part 11 delivers the selection signal for detection level to a power supply voltage detecting part 1. Thus, a level deciding signal is delivered to the part 11. An OFF signal is delivered when it is discriminated that the battery voltage cannot be kept under a normal working state. Then, the power supply stop signal is delivered to the part 1 and a power supply voltage stabilizing part 6. Thus, no power is supplied to each part.