A circuit board includes a substrate, a first ground electrode group, and a first pair of signal electrodes. The first ground electrode group includes a plurality of first ground electrodes, where each of the plurality of the first ground electrodes is disposed at a corresponding one of vertexes of a first rectangular area in a surface of the substrate. the first pair of signal electrodes is disposed in the first rectangular area and is arranged in a first direction parallel to a side of the first rectangular area.