Connection portions (225UP through 225WP) to which upper arm control terminals (320UU through 320UW) are connected are disposed at a first edge portion of a drive circuit board (22). And connection portions (225UN through 225WN to which lower arm control terminals (320LU through 320LW) are connected are disposed at a second edge portion of the drive circuit board (22). Upper arm implementation regions (227UP through 227WP), lower arm implementation regions (227UN through 227WN), and a low voltage pattern region (228) in which photo-couplers (221U through 221W) are implemented are formed in the board region between these board edge portions. And signal wiring (40U) that transmits a control signal from a photo-coupler (221U) to an implementation region (227UN) is formed in a conductor layer that is a lower layer than the conductor layer in the lower arm implementation region in which the lower arm driver circuit is implemented.