PURPOSE: To prevent the data breakdown of a first device by registering in advance a pair of the name of the first device and battery validity in a second device, and informing the service life of a battery backup battery of the first device to an operator with a display device, etc.

CONSTITUTION: In the nonvolatile or backed-up volatile storage device of the second device (personal computer) 1, a pair of the name of the first device (RAM card) and battery validity is registered in advance. In such a state, the RAM card is inserted into a RAM card slot 4, thereafter, by starting the personal computer 1 and operating a key of a keyboard 3, an instruction and information are inputted, and the inputted information is displayed on the screen of a liquid crystal panel (LCD) 2. Also, for the purpose of backup, the RAM card battery is integrated, and at the time of service interruption, etc., data is held by a battery voltage immediately. Moreover, the service life of the battery is informed to an operator by the LCD 2 or an alarming device. In such a manner, the data breakdown of the RAM card can be prevented.