PURPOSE: To provide the signal processor for re-transmission in the common viewing system capable of conversion for each frequency when input and output channels are the same for frequency conversion.

CONSTITUTION: A high frequency is adopted for an intermediate frequency band, an inputted television broadcast signal is mixed with a 1st local oscillation signal, the result is separated into a video 1st intermediate frequency signal and an audio 1st intermediate frequency signal by a separator 11, they are amplified and adjusted respectively and then synthesized by a synthesizer 14. The synthesized signal is mixed with a 2nd local oscillation signal and a 3rd local oscillation signal being a sum signal or a difference signal between the 1st local oscillation signal and the 2nd local oscillation signal is mixed with the mixed signal and the result is outputted from an output terminal 21 as an output signal.