A potential isolation element is provided separately from a diode. An n-type low-concentration region is formed on a P-type layer. A first high-concentration N-type region is positioned in the n-type low-concentration region and is connected to a cathode electrode of the diode. A second high-concentration N-type region is positioned in the n-type low-concentration region, is disposed to be spaced from a first second-conduction-type high-concentration region, and is connected to a power supply interconnection of a first circuit. A first P-type region is formed in the n-type low-concentration region, and a bottom portion thereof is connected to the P-type layer. A ground potential is applied to the first P-type region, and the first P-type region is positioned in the vicinity of the first high-concentration N-type region.