PURPOSE: To provide a high rigidity and lightweight fin for board with fine appearance by forming a reinforced plastic layer, with woven fibers arranged as reinforcement, around a core material approx. in the form of fin made from a hard forming resin.

CONSTITUTION: To fabricate a fin for board, core material is previously prepared consisting of hard foamed polyurethane resin, in which a hole reinforcing plastic 3 is embedded in order to mount the fin on the board body. Two pieces of woven carbon fibers cut previously approx. in the form of fin are placed in either of an upper and a lower die in such an angle relation as 0 deg and 45 deg relatively, followed by placing of a core 1, and thereover two pieces of woven carbon fibers also cut into approximate fin form are put surface- symmetrically to the opposite side in the angle relation of 0 deg and 45 deg, that is followed by shutting of the dies tightly. Unhardened epoxy resin as a mixture of a main material and a hardening agent is poured from a pouring port into the gap between the core 1 and dies and left to harden. Thus a plastic layer 2 reinforced with carbon fibers is accomplished.