A circuit board (3) is provided with a first rigid part (11) having a power system electronic component mounted thereon, a second rigid part (12) having a control system electronic component mounted thereon, and a thin flexible part (13) connecting the first and second rigid parts to each other. The flexible part (13) is provided with a plurality of conductive wires (27) conducted with the electronic components of the first and second rigid parts (11, 12). A non-conductive metal pattern (33) that is a dummy pattern is formed along an outer edge (13a) of the flexible part (13). By the non-conductive metal pattern (33), the disconnection of the conductive wires (27) due to cracking is suppressed.