To provide a method enabling simulation voltage/current signals to be synchronized on a terminal-by-terminal basis without connecting testers to each other disposed on respective terminals of a power transmission system, thereby enabling a counter test of protective relays to be simply performed.

Simulation voltage or simulation current is inputted from testers 4 into respective protective relays 1, the phase of the simulation voltage or of the simulation current of each tester 4 is adjusted based on a displayed phase difference of the protective relay 1, and the frequency of the simulation voltage or of the simulation current of each tester 4 is adjusted based on the time lapse of the displayed phase difference of the protective relay 1. This enables the simulation voltages or the simulation currents to be synchronized and their frequencies to be equalized to perform a counter test of the protective relays.