PURPOSE: To prevent disappearance of stored information and data in an RAM card because of exhaustion of a battery by notifying the expiration of validity of a memory protection battery in the RAM card by a battery change alarm display or a an alarm sound.

CONSTITUTION: The date of starting the use is written into a specified corresponding area in an RAM card 111 with a keyboard 104 at the time of starting the use there of 111 or at the time of changing a memory protection battery and a registered validity bit is set. An interrupt for checking the validity of the memory protection battery is generated periodically after a prescribed time passes. After the generation of the interrupt, the date of starting the use registered in the card is compared with the current date of a calendar clock 102 and when coincidence or excess is found in validity therebetween, an alarm display is given on an LCD display panel 103 or an alarm sound is generated through a sound control 106. When the validity is not exceeded, the number of residual days is displayed on the panel 103 by the operation of the keyboard 104. This enables the prevention of disappearance of information or data in the card due to the expiration of the validity of the battery.