PROBLEM TO BE SOLVED: To obtain a voltage detection circuit which prevents data from being lost due to the supply shortage of a data holding voltage due to the consumption or the like of an auxiliary battery when the main battery of a memory card is replaced by a method wherein a voltage detector or the like which detects the voltage of the auxiliary battery is installed. SOLUTION: When a main battery holder 31 is mounted on a body, a switch botton 63 is pressed to a protrusion part 39a, and a switch 61 is set to an OFF state. When the main battery holder is taken out form the body, knob parts 31a, 31b are sandwiched so as to be moved to the center, the protrusion part 39a is moved to the center, the switch botton 63 is released from its pressure, and the switch 61 is set to an ON state. When the switch 61 is turned pn, the voltage of an auxiliary battery 25 is detected by a voltage detector, and an LED 59 emits light when the voltage of the auxiliary battery 25 is lower than a prescribed voltage. That is to say, when such a function is installed at a memory card, the voltage of the auxiliary battery 25 can be detected, and it is possible to prevent data in a volatile memory form being erased when a main battery 19 is replaced.
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