A printed wiring board of the present disclosure includes a power supply layer and a ground layer. A power supply layer pattern to be formed partially on the power supply layer includes a branch and a power supply layer electrode. The branch is a direct-current power feeding path for connecting adjacent electromagnetic band gap (EBG) unit cells, and the power supply layer electrode is connected through a slit provided along the branch. A capacitive coupling element disposed to oppose the power supply layer electrode with an interlayer being provided therebetween has a structure in which the EBG unit cells are disposed at regular intervals, the EBG unit cells being connected to the branch in the power supply layer pattern through a via.