A transmission system of an embodiment is provided with an active transmitter, a backup transmitter, and a system controller to integrally control the active transmitter and the backup transmitter. The backup transmitter is provided with a setting table which stores a setting value relating to a frequency and a level of a signal outputted from the active transmitter, a power amplifier to amplify an input signal and output an amplified signal, and a modulator/exciter which converts, based on the setting table, the input signal into a modulation signal of a prescribed broadcast type in which nonlinear distortion by the power amplifier has been compensated. The system controller, at the time of adjusting the output level of the active transmitter, controls the backup transmitter so that content of the setting table of the backup transmitter becomes a setting value corresponding to the adjusted output level.