To avoid danger after execution by using an extension type anchor for firmly fixing a root ball even if a planting part of a tree is in the weak ground, readily burying the root ball by placing the anchor and forming a structure not exposing most of works to the surface of the earth.

Resistant plates 14 joined in two through a stay anchor 13 are connected to each of plural fixing plates 2 fixed at the upper side of a root ball 9. The upper ends of each fixing plate 2 are mutually connected by a binding rope 10. The resistant plates 14 are placed so that each fixing plate 2 pressures soil on the upper side of the root ball 9 and the resistant plates 14 are buried in an extended state in the ground.