In a memory comprising a memory device (24), a voltage gener­ation circuit (6) converts a power source voltage supplied from an external device and generates a substrate bias volt­age. The external device serves to read from, and write into, said memory device (24) and to supply operation power to said memory device (24). Further provided are a first battery (17c) for supplying said substrate bias voltage to said memory de­vice (24) and a second battery (17a, 17b) for supplying power to said memory device (24), when the operating power is not supplied from said external device.