PURPOSE: To prevent the volatilization of data accompanied by the consumption of a data holding battery, by a method wherein, a back-up battery having a voltage higher than the data holding battery is provided in a memory card storage case body, and connection terminals conducting to this battery and being connected to external power source terminals of a memory card are provided.

CONSTITUTION: When a memory card 20 is inserted into a card storage part 3 of a case 1 to be stored, external power source terminals 26 and 27 of the memory card 20 are respectively brought into contact and connected with connection terminals 5 and 6 provided by conducting to a back up battery 4, and a power supply is started from the back-up battery 4 through these terminals 26, 27, 5, and 6. At this time, because a voltage held by the back-up battery 4 is higher than that of a data holding battery 22, a reverse bias acts to a battery-side diode 23 in the memory card 20 and results in the interruption of a power supply from the data holding battery 22 to a RAM memory 21. In this manner, a power from the back-up battery 4 is supplied to the RAM memory 21 through a power source side diode 25.