An on-vehicle transmission system includes: a path part configured to transmit a radio signal received from the antenna side, to the on-vehicle-device side; an on-vehicle-device-side circuit unit including a plurality of wireless circuits configured to receive radio signals in frequency bands different from each other; and a power supply circuit configured to supply power from the on-vehicle-device side to a circuit on the antenna side via the path part. The plurality of wireless circuits are connected in series via a transmission line configured to transmit a radio signal, and are respectively connected to the plurality of on-vehicle devices via the transmission line configured to transmit a radio signal. The on-vehicle-device-side circuit unit splits the radio signal received from the path part and provides resultant radio signals to the respective wireless circuits.