To efficiently perform mounting and removal of a nut setting cap using an indirect tool, wherein the cap prevents slackening of a nut to fasten a pin insulator attached to an arm metal piece of an electric pole.

A mounting/detaching tool 10 is to mount and remove a nut setting cap 7 to be installed removable at the tip of an indirect tool 25, is made from a thin board 11 having any desired shape, and provided at one side edge with a fit groove 12 opening 14 at the side edge and admitting insertion of a threaded pin 3 of a pin insulator 1, wherein the cap 7 is inserted and held in the backmost part in the groove 12, and a holding part 15 is provided having a diameter smaller than the flange 9 at the top of the cap 7.