When a bias voltage of a substrate is generated, an output voltage of a charge pump is controlled at an appropriate level, resultingly reducing a consumption current. The charge pump generates a predetermined output voltage from a predetermined DC power supply. A clock generator outputs a clock for operating the charge pump. A voltage monitoring unit monitors the output voltage of the charge pump and controls the clock output from the clock generator such that the output voltage is maintained within a predetermined range. A voltage regulator generates the bias voltage from the output voltage of the charge pump.