The power supply layer electrode 421′ and the capacitive coupling element 43′ are capacitively coupled with each other through the insulating layer 5. On the other hand, a portion of the power supply layer electrode 421′ is connected to the branch 422′ through the adjacent power supply layer wire 423. At the same time, the leading end of the capacitive coupling element wire 432′ extending from the capacitive coupling element 43′ is connected to the branch 422′ through the via. The via is formed by an electrically conductive material such as copper.

The equivalent circuit of the resonance circuit portion included in the EBG unit cells 41′ configuring the EBG structure 4′ is identical to the equivalent circuit of the resonance circuit portion included in the EBG unit cells 41 configuring the EBG structure 4 illustrated in FIG. 3. In the power supply layer pattern 42′, the power supply layer wire 423 that is not present in the power supply layer pattern 42 is formed. Further, in the capacitive coupling element 43′, the path of the capacitive coupling element wire 432′ is made to be longer than the path of the capacitive coupling element 43. For this reason, the inductance Lw that is a sum total of the inductance components of both of them can be made to be larger in EBG unit cells 41′ than in EBG unit cells 41. Since the coupling capacitance Cs from all appearance can be increased by increasing the inductance Lw, as a result, the parallel resonance frequency can be made to be low. This means that the EBG unit cells 41′ can be further downsized, and thus the EBG structure 4′ can be further downsized.