PURPOSE: To lessen necessary components and devices by simulating a state of arrival of light burst signals of different signal levels from a plurality of transmission sources by controlling an output level for each burst of a light test signal.

CONSTITUTION: A burst signal generator 1 generates an electric signal for a test in the shape of a burst. An electro-optical converter 2 converts this electric signal into a light signal and sends it out to an optical fiber transmission line 5. By adjusting an output level of the converter 2 by the control of a level control part 3, at this time, input of light burst signals of indefinite signal levels from a plurality of transmitting-receiving devices, e.g. subscriber's devices, is prepared by simulation. Accordingly, a state wherein the light burst signals are inputted to the transmission line 5 at a loss of 10 dB from one transmitting- receiving device and at a loss of 20 dB from another transmitting-receiving device, for instance, is simulated. The light burst signals transmitted through the transmission line 5 are inputted to a signal measuring unit 7 through a light-receiving part 6 The measuring unit 7 measures the characteristics of hard ware ranging from the transmission line to the light-receiving part.