To obtain a closed-form reinforcing material made of a fiber-reinforced resin, having excellent corrosion resistance and lightweight properties, being nonmagnetic, effectively usable as various reinforcing members and to provide a method for producing the closed-form reinforcing material.

A yarn comprising a high-strength/high-elasticity impregnated with a matrix resin is wound on a molding form in a loop shape for several times. After the winding, the matrix resin is cured. After the curing, the yarn wound in a loop shape and molded is released from the molding form to give a closed-form reinforcing material R made of the fiber-reinforced resin.