A substrate bias voltage generator circuit has a substrate bias voltage detector circuit, a substrate bias driver circuit, and a charge pump circuit. the substrate bias voltage detector circuit detects a substrate bias voltage applied to a semiconductor substrate and outputs a substrate bias voltage detection signal. The substrate bias detector circuit includes a P-channel transistor with a gate terminal and an N-channel transistor with a substrate terminal, both terminals being connected to the semiconductor substrate and the substrate bias voltage which is a back bias for the N-channel transistor. The substrate bias driver circuit is responsive to the substrate bias voltage detection signal outputted from the substrate bias voltage detector circuit, and outputs a drive signal when the absolute value of the substrate bias voltage is equal to or smaller than a predetermined value, and stops outputting the drive signal when the absolute value of the substrate bias voltage is larger than the predetermined value. The charge pump circuit is responsive to the drive signal from the substrate bias driver circuit, and generates the substrate bias voltage.