To provide a rope extension method which can extend a rope without interfering with obstacles even if there are obstacles such as electric wires.

In the method which pulls out a rope 3 wound around the drum 5 of a first pilotless helicopter 4 by letting the pilotless helicopter 4 fly in the air where the tip end part 3 of the rope 3 wound around the drum 5 of the first pilotless helicopter 4 is fixed to a specified position, in a space between the specified position and the first pilotless helicopter 4, let a second pilotless helicopter 8 hover in the air above an electrical wire 6, the rope 3 is suspended by means of a ring 11 provided for the second pilotless helicopter 8, and the rope 3 is prevented from interfering with the electric wire 6 when the rope 3 is extended.