To locally reinforce the part within a hollow structural member hard to reach by conventional technique.

In a method for reinforcing the specific place of a structural member, a bending tube equipped with a resin coating in a state before expansion is used. A resin is desirably thermally expansible. The coating may be arranged at the specific place on the line of the bending tube. The bending tube is inserted from a curved route to coincide with the shape of a member to be reinforced. When the place having the coating on the tube reaches a predetermined position, the tube is arranged as it is. After heating, the resin is expanded several times its initial vol. and a structural cavity is filled at that place.