A reinforcing material, comprises a reinforcing resin sheet which is unhardened or semi-hardened to be flexible prior to its use; a high tensile-strength fiber for reinforcing the resin sheet in its longitudinal direction; a low tensile-strength fiber for reinforcing the resin sheet in its transverse direction; and an expandable material narrower than the resin sheet. The expandable material is flexible, at least before the reinforcing material is used. The expandable material is made of a material which can expand to form a bead-like projection before the resin sheet is hardened. The expandable material is fixed to the resin sheet. The resin sheet has its edge portions extending beyond the expandable material so that the underside surface of the edge portion constitutes a surface which can be affixed to the surface to be reinforced.