A printed circuit board, comprising: a printed wiring board comprising a power layer having a wiring-shaped power pattern formed therein and a ground layer having a plane-shaped ground pattern formed therein, the ground layer being opposed to the power layer across a dielectric layer; one or more semiconductor devices (102, 103) mounted on the printed wiring board, the one or more semiconductor devices each having a power terminal connected to the power pattern and a ground terminal connected to the ground pattern; and a power supply member, mounted on the printed wiring board, for supplying DC power to the one or more semiconductor devices via the power pattern and the ground pattern, wherein the ground pattern includes at least one defect portion, where a pattern is missing in the ground layer, formed therein in a first ground region, the first ground region being defined by projection of the power pattern onto the ground layer as viewed from a direction perpendicular to a surface of the printed wiring board, wherein, in the first ground region, the at least one defect portion forms a region that is narrower than the power pattern, said region communicating a first region (R11, R12), defined by projection of one of the semiconductor devices onto the ground layer as viewed from a direction perpendicular to the surface of the printed wiring board, and a second region, defined by projection of the power supply member onto the ground layer as viewed from a direction perpendicular to the surface of the printed wiring board, and wherein the at least one defect portion is formed at a position that does not intersect with a line segment connecting a gravity point of a contour of one of the semiconductor devices, resulting from projection of the one of the semiconductor devices onto the ground layer as viewed from a direction perpendicular to a surface of the printed wiring board, and a gravity point of a contour of the power supply member, resulting from projection of the power supply member onto the ground layer as viewed from the direction perpendicular to the surface of the printed wiring board. a printed wiring board comprising a power layer having a wiring-shaped power pattern formed therein and a ground layer having a plane-shaped ground pattern formed therein, the ground layer being opposed to the power layer across a dielectric layer; one or more semiconductor devices (102, 103) mounted on the printed wiring board, the one or more semiconductor devices each having a power terminal connected to the power pattern and a ground terminal connected to the ground pattern; and a power supply member, mounted on the printed wiring board, for supplying DC power to the one or more semiconductor devices via the power pattern and the ground pattern, wherein the ground pattern includes at least one defect portion, where a pattern is missing in the ground layer, formed therein in a first ground region, the first ground region being defined by projection of the power pattern onto the ground layer as viewed from a direction perpendicular to a surface of the printed wiring board, wherein, in the first ground region, the at least one defect portion forms a region that is narrower than the power pattern, said region communicating a first region (R11, R12), defined by projection of one of the semiconductor devices onto the ground layer as viewed from a direction perpendicular to the surface of the printed wiring board, and a second region, defined by projection of the power supply member onto the ground layer as viewed from a direction perpendicular to the surface of the printed wiring board, and wherein the at least one defect portion is formed at a position that does not intersect with a line segment connecting a gravity point of a contour of one of the semiconductor devices, resulting from projection of the one of the semiconductor devices onto the ground layer as viewed from a direction perpendicular to a surface of the printed wiring board, and a gravity point of a contour of the power supply member, resulting from projection of the power supply member onto the ground layer as viewed from the direction perpendicular to the surface of the printed wiring board.