PURPOSE: To mutally improve the degree of freedom in the movement of a work station or a printer by distributing and disposing a pair of light transmitting/receiving unit generating a bidirectional transmission line by means of a spatial transmitting light beam on the sides of the work station and the printer, and giving and receiving signals between both units through light transmitting space.

CONSTITUTION: Electrical/optical signal conversion parts 5A and 5B constitute a pair of the light transmitting/receiving units generating the bidirectional transmission line through optical transmission space. Since a pair of the light transmitting/receiving units are disposed while they are distributed to the side of the work station 1 and that of the printer 2, the signals are transmitted are received between both units through optical transmission space. Thus, the setting positions of the work station 1 and the printer 2 can freely be moved in space where optical transmission is attained without being restricted by a cable, and connection between the work station 1 and the printer 2 can easily be executed without being troubled by the cable.