PURPOSE: To obtain a small-sized light counting resister having high reliability and capable of detecting even the range of a current value, by connecting plural sets of resistors and discharge gaps to the earth side terminal of a lightning arrester or a protective gap.

CONSTITUTION: The high voltage terminal of a discharge counting register is connected to the earth terminal of a lightning arrester 21 and connected to three resistors 22 classified by a current value range having different resistance values. Discharge gaps 23 are respectively connected to the resistors 22 in parallel and one terminals of optical fibers 24 are arranged to the arc generating parts of the discharge gaps 23 and the other terminals thereof are connected to optical trigger counters 25. When the lightning arrester 21 is operated, a discharge current flows to the ground through the resistors 22. At this time, voltages are generated between the terminals of the resistors 22 corresponding to the discharge current value of the lightning arrester 21 and only the discharge gap 23 having current sensitivity equal to or less than the current value discharges to generate an arc. This generated arc light reaches the trigger part of the corresponding optical trigger counter 25 through the optical fiber 24 to operate a counter.