As illustrated in FIG. 5, the circuit board 33 has a slit 82 linearly extending from a part of the peripheral edge between the first peripheral edge 41 and the second peripheral edge 42, in parallel with the second peripheral edge 42 so as to pass between the first insertion hole 51B and the second insertion hole 52B that is closest to the first insertion hole 51B. The slit 82 is formed so as not to interfere with the patterns and the electronic components on the circuit board 33. A distance L1 between a center of the first insertion hole 51B and a center of the second insertion hole 52B is shorter than a distance L2 between a center of the first insertion hole 51A and a center of the second insertion hole 52A because the ground line 80 is desirably located physically close to the busbars 57.
