To reduce the cost necessary for the operation scuh as maintenance fee for deducing a measurement time, and to simplify a device configuration by testing many light lines with one light pulse tester at the same time.

Two adjacent light lines are connected gradually by the use of multiplexer/demultiplexer photo-couplers so that a 1st light line 86 and a 2nd light line 87 are connected to a multiplexer/demultiplexer photocoupler 21 at a right end, and the line 87 and a 3rd light line 88 are connected to a multiplexer/demultiplexer photocoupler 22 at a left end in plural light lines for connecting optical transmitter devices 1A and 2A, an optical pulse tester 12 is connected to the left end of the line 86 through the use of a multiplexer/ demultiplexer photocoupler 20 and each light line is tested by using only one test beam of the tester 12.