PURPOSE: To detect easily the breaking of an element wire from the ground and secure the safety of operation by utilizing the roation or shift of a power transmission line for the detection of the breaking.

CONSTITUTION: A plastic or metallic ring 2 is fixed near the clamping part 1 of an electric cable 3. If the element wire 31 of the electric cable 3 is broken in the clamp 1, the electric cable 3 rotates, so the ring 2 is colored (e.g. upper half part is colored in red) to find easily that the ring is rotating, thus detecting the breaking of the element wire. Consequently, the detection from the ground is facilitated and secured and it is not necessary to climb a steel tower and perform inspecting operation, so the safety of operation is secured together with the reduction in maintenance inspection cost.