An electromagnetic bandgap structure includes: first conductive plates, placed on a first planar surface, in which the first conductive plates are lined up in a first direction; second conductive plates, placed on a second planar surface and arranged at an area corresponding to an area in which the first conductive plates are disposed, in which the second conductive plates are lined up in the first direction; a first stitching via, electrically connecting any two adjacent conductive portions with each other and in which the two adjacent conductive portions are lined up in a direction that is different from the first direction on the first planar surface; and a second stitching via, electrically connecting any two adjacent conductive portions with each other and in which the two adjacent conductive portions are lined up in a direction that is different from the first direction on the second planar surface.