Abstract: A CPU checks whether a content of a battery insertion detecting RAM has a predetermined bit configuration and whether a flag during battery check is set after power on reset. If neither the RAM has the bit configuration nor the flag is set, the flag is set and then a dummy current is caused to flow into a dummy load. When power consumption is high, the power supply voltage greatly drops within a predetermined period of time after the dummy load is turned on and therefore the voltage sensing IC detects the voltage drop and the CPU is reset. Since the CPU initializes all ports if it is subjected to hard reset, the current is stopped to flow into the dummy load and the power supply voltage is recovered. After the hard reset, the CPU checks the content of the RAM and the flag. Since the flag continues to be set, the CPU determines that the battery runs down and performs a battery run-down operation. When the battery is loaded, the RAM usually has a predetermined bit configuration.