a phase comparator detecting a phase shift between a changing point of data transmitted through an electro/opto converter and a changing point of data received through an opto/electro converter; and

a controller controlling delay of the transmitted data so that the phase shift outputted by the phase comparator becomes equal to a value which minimizes a receiver sensitivity degradation due to crosstalks between a transmitter portion and a receiver portion, and outputting a difference between the phase shift outputted from the phase comparator and a value which minimizes the receiver sensitivity degradation, and a variable delay circuit controlling delay of the transmitted data by the difference.