On the other hand, as understood form FIG. 13, in the lateral direction, it is preferable that the diameter size of the via 225 is smaller than an interval size (the predetermined interval) between the magnetic pieces 141 adjacent to each other. This is because of the following reason. If the diameter size of the via 225 is larger than the predetermined interval in the lateral direction, only one of the magnetic pieces 141 adjacent to each other may be remarkably removed in part when a formation position of the via 225 is displaced by a manufacturing accidental error. As a result, the desired magnetic characteristics for the circuit board 20 may not be obtained.

As understood from FIG. 12, when the positioning member 143 is cut by forming the via 225, remaining portions of the positioning members 143 remain connected to adjacent surfaces of the magnetic pieces 141 adjacent to each other, each of the remaining portions has a cut mark 145. When the position of the via 225 is displaced by a cause such as manufacturing variation, there is a case where the cut marks 145 remain on the adjacent surfaces of the magnetic pieces 141 adjacent to each other. At any rate, the via 225 is in surface contact with the cut marks 145.