A first circuit and a second circuit having the same voltage-current characteristics are connected in series between a power supply potential node and a ground potential node. Each of the first and second circuits includes as a load element a MOS transistor formed on a semiconductor substrate having a triple-well structure. A first reference potential is provided from the first circuit. A third circuit and a fourth circuit having the same voltage-current characteristics are connected in series between the power supply potential node and the ground potential node. Each of the third and fourth circuits includes as a load element a MOS transistor formed on the semiconductor substrate having the triple-well structure. A second reference potential is provided from the third circuit. The first reference potential is applied to the gate of an n-channel MOS transistor connected between the power supply potential node and an output node. The second reference potential is applied to the gate of a p-channel MOS transistor connected between an output node and the ground potential node. An intermediate potential between the power supply potential and the ground potential is provided from the output node. An auxiliary drive circuit operatively coupled to the output node provides increased current driving capability for driving the output node to the intermediate potential.