To enable a highly reliable serial transmission at a low cost with a small circuit scale by preventing multistage propagation of a pathological signal (pattern data with maximum component, etc.), and minimizing a cumulative increase of jitters in the multistage relaying.

A repeater 160 supplies data Din transmitted by a coaxial cable to an equalizer 161 to compensate attenuation characteristics and then a D flip-flop 163 latches the data by using a serial clock signal SCK reproduced from the data Din to obtain reception data RSD. The reception data RSD is converted by a converter 164 from an NRZI(non-return-to-zero inverted) code to an NRZ(non-return-to zero) code and descrambled by a descrambler 165 to obtain serial digital data SDr. The data SDr is scrambled by a scrambler 166 and further converted by a converter 167 from the NRZ code to the NRZZI code to obtain data Dout to be resent, so that the data Dout is sent out to the coaxial cable through a cable driver 168.