To provide a readily executable supporting tool for a tree capable of preventing the tree from falling by an external force such as a wind without protruding bodies other than the tree from the top surface of the ground according to a simple constitution without arousing a fear of inflicting an injury, etc., on a passerby even when approaching the tree and without inhibiting the healthy growth of the tree.

This supporting tool for a tree is obtained by detachably securing a drainboard-shaped lid member 2 divided into plural parts having female screw holes bored in the vertical directions in an opening 20a for enabling the tree to pass therethrough and an edge material 5 near the opening 20a to an opening 10c of a curb 10 arranged around the tree, closing the opening 10c of the curb 10 with the drainboard-shaped lid member 2, arranging pressing members 8 at positions on the lower side of the female screw holes bored in the edge material 5 near the opening 20a of the drainboard-shaped lid member 2, screwing bolts 9a from the upper side of the female screw holes thereinto and pressing the top surface of the pressing members 8 with the tip of the bolts 9a.