PURPOSE: To evaluate the characteristic of a repeater by using a pulse trio signal as a trigger signal for forming a loopback loop and inputting an evaluation measuring signal via a repeater in the loopback loop formed in this way to a line measuring instrument.

CONSTITUTION: A pulse trio signal having a specific frequency component assigned to a repeater 331 is sent from a line measuring instrument 34 at first, which detects whether or not the pulse trio signal is looped back normally from the repeater 331. When the pulse is normally looped back, the instrument 34 sends an evaluation measuring signal for evaluating the characteristic for the repeater 331 to measure the characteristic. Then the pulse trio signal having a specific frequency component assigned to a repeater 338 is sent from the line measuring instrument 34, which detects the loopback to measure the characteristic of the repeater 338. Similarly, the measurement of the characteristic of each repeater is sequentially repeated in the direction of a repeater 33n.