PURPOSE: To enable to swiftly rise the potential of the substrate after a power source is turned ON, and moreover, to decrease the power consumption by a method wherein an oscillating voltage generating circuit of an oscillation frequency is actuated when the potential of the substrate is set and another oscillating voltage generating circuit of an oscillation frequency, which is different from that of the aforesaid oscillating voltage generating circuit, is actuated after the potential of the substrate is set.

CONSTITUTION: A ring oscillator 4 alone of an oscillation frequency of 20MHz is actuated by a signal, which is sent from a controller circuit 6, in a time shortly after a power source has been turned ON. When a prescribed time lapsed after the turning ON of the power source, the operation of the oscillator 4 is made to stop by the circuit 6 and a ring oscillator 5 of an oscillation frequency of 200kHz is actuated. On the other hand, a switching circuit 7 receives a signal, which is sent from the circuit 6, performes a switching operation to correspond to the abovementioned operation and feeds the output of the oscillator 4 or the oscillator 5 to a charging pump circuit 8. The output of the circuit 8 is fed to the substrate of an IC wafer as bias voltage. According to this constitution, the potential of the substrate can be brought to the prescribed value in a comparatively short time after a power source is turned ON. A power consumption of 1mA or thereabouts is needed during this time, but the power consumption can be suppressed up to that of 30μA or thereabouts after that time by the operation of the oscillator 5.