PURPOSE: To provide adjustability for the length of discharging gap easily by fitting an lightening protection insulator to a cap metal piece of an anti-tension insulator in such a way as facing down, and by arranging a discharge electrode supported on the jumper wire side situated on the lower side and a discharge electrode of the lightening protection insulator in such a way as oppositely.

CONSTITUTION: A lightening protection insulator 26 is fitted to a cap 10 of a suspended insulator 7 in such a way as facing down, and a discharge electrode 36 installed at the bottom of this insulator 26 and a discharge electrode 23 installed on the jumper wire 18 side are faced oppositely. The in-air insulation gap between the insulator 26, a steel tower, and the jumper wire 18 in the upper phase is retained sufficiently. When a surge current due to lightening shock flows through a power transmission line 15, the current is flashed over to the discharge electrode 36 on the grounded side via the jumper wire 18 and the discharge electrode 23 on the charge side to flow through a current restricting element 32 inside the insulator 26, so as to flow to the steel tower via a support arm 1 to be then discharged. The continuous current to be generated thereafter is shut by the element 32 and the in-air discharge gap G. Thereby the in-air insulation gap is secured to allow adaptation to an existing steel tower.