A transmission line board includes an insulating substrate including a first principal surface, first and second signal lines, first and second signal electrodes, which are provided at the insulating substrate. The first signal electrode is connected to the first signal line, and is connected by capacitive coupling to a different circuit board. The second signal electrode is connected to the second signal line, and is connected to the different circuit board via a conductive binder. The first signal line is provided to transmit a signal in a first frequency band, and the second signal line is provided to transmit a signal in a second frequency band lower than the first frequency band.