PURPOSE: To reduce a leak current from a RAM part by connecting the output of a constant voltage circuit connected between a charge circuit and a battery or a capacitor to the capacitor and the RAM part, and at the time of interrupting the battery, interrupting also the constant voltage circuit.

CONSTITUTION: The output of the constant voltage circuit D connected between the charge circuit B and the battery A or the capacitor E is connected to the capacitor E and the RAM part F. When power is supplied to the RAM part F through the circuit D, a leak current from the RAM part F can be extremely reduced and the circuit D can be constituted of transistors(TRs) having the same VT as a CPU part or the like. At the time of memory protecting operation, i.e., the interruption of the battery A, the circuit D can be interrupted and no unnecessary current flows. Since the output voltage of the circuit D is set up by using a MOS TR VT as a reference voltage, the output voltage is changed while interlocking with the variation of the minimum operation voltage of the RAM part F, so that the operation of the RAM part F can be conveniently guaranteed.