A field plate electrode is repetitively disposed in a folded manner or a spiral shape in a direction along an edge of a first circuit region. A coupling transistor couples a first circuit to a second circuit lower in supply voltage than the first circuit. A second conductivity type region is disposed around the coupling transistor. A part of the field plate electrode partially overlaps with the second conductivity type region. The field plate electrode is electrically coupled to a drain electrode of the coupling transistor at a portion located on the first circuit region side from a center thereof in a width direction of the separation region. A ground potential or a power potential of the second circuit is applied to the field plate electrode at a portion located on the second conductivity type region side from the center.