To solve such a problem wherein a polyester resin putty is difficult to apply thickly, and if forcibly applied, the shrinkage increases and the weight rises.

1 to 5 pts.mass of glass fibers cut into 1 to 10 mm and 30 to 70 pts.mass of hollow beads as a lightweight powder material are added to 100 pts.mass of an unsaturated polyester resin. Further, 1 to 6 pts.mass of a curing accelerator cobalt is added to form a base agent. 1 to 3 pts.mass of a hardener such as Permek to be used at use time of the base agent is added to 100 pts.mass of the unsaturated polyester resin contained in the base agent.