A circuit board is provided in which a transmission loss is reduced. The circuit board includes a first layer; a transmission line disposed on the first layer; and a second layer stacked with the first layer. The second layer includes a first region, which is constructed of a first material, corresponding to a position of the transmission line, and a second region, which is constructed of a second material having a permittivity that is different from that of the first material, corresponding to the position of the transmission line.