PURPOSE: To make the inspection possible under the assembling state without giving any influence upon the power distribution system, by making it possible to connect a testing equipment to either of a trouble searching device for successive selections and a trouble searching device for loop points through a cable.

CONSTITUTION: In case of the test for a trouble searching device for successive selections, terminals (a)W(g) and r1 of a testing equipment 1 are connected to corresponding terminals of searching device through cables. Locking of the trouble searching device is released by, for example, a reset circuit 15 without breaking a section switch, and a reset push-button switch PBS3 is depressed to reset a function discriminating display part 8, a counting circuit 9, and a counting display part 10 of the testing equipment 1. In case of the test for a trouble searching device for loop points, terminals (a)W(f) and (h)W(l) of the testing equipment 1 are connected to corresponding terminals of the trouble searching device, and a selecting switch of the testing equipment 1 is switched to the side of the test for the trouble searching device for loop points, and the trouble searching device for loop points is testing similarly to the trouble searching device for successive selections.