PROBLEM TO BE SOLVED: To provide a method for ensuring stability of working posture on a tree free from burden on exchanging lanyard by forming a double rope system and a lanyard system with one long rope.SOLUTION: In the method for ensuring stability of working posture on a tree, a rope device 1 is used. In the rope device 1, a first connector 4A is attached to one end part of one long rope 2. A first length adjuster 3A is attached to the long rope 2 at a position apart from the first connector 4A by a certain length. A second connector 4B is attached to the first length adjuster 3A. The part of the long rope extending nearly from the first connector 4A to the first length adjuster 3A provides a double rope system DRS. A second length adjuster 3B and a third length adjuster 3C are attached at the positions on the long rope 2 apart backward from the first length adjuster 3A with an interval of a certain length. Third and fourth connectors 4C, 4D are attached to these second and third length adjusters 3B, 3C. The part of the rope extending from the second length adjuster 3B to the third length adjuster 3C provides a lanyard system LYS.
