PURPOSE: To connect lots of slave stations in cascade with simple constitution by sending a multiplex electric signal to plural slave stations connected in cascade from a master station and allowing a slave station to separate and extract a signal to its own station and to send a signal with a different wavelength depending on each slave station.

CONSTITUTION: Lots of slave stations 2001, 2002∼are connected to one master station 100 in cascade by an optical fiber 11. Then an attitude control signal from a controller 104 to cameras 2041, 2042 of each slave station is multiplexed by a multiplexer 105, converted into an optical signal in a wavelength λ5 and sent. A multilexer/demultiplexer 201 of a slave station 200 acts like a demultiplexer to an optical signal of the wavelength λ5 and a multiplex signal from the master station 100 is received by a photodetector 202. After the signal is converted into an electric signal, the result is given to a demultiplexer 205, from which a signal assigned to its own station is extracted. Further, a picture signal from the camera 204 is converted into optical signals λ1, λ2∼different from each slave station by an optical transmitter 203 and sent to the master station.