PURPOSE: To enhance safety and efficiency of insulator coupling work by eliminating the intervention of worker.

CONSTITUTION: An object measuring unit 10 detects the position of a hole at the coupling part of an insulator 51 to be coupled three-dimensionally. A processor 40 controls a robot 30, based on the position of hole thus detected, to fit a coupling insulator 52 to the insulator 51 to be coupled and then controls a robot 20 to insert a cotter 53 into the coupling part of the insulators 51, 52.