PURPOSE: To provide a reinforcing material useful to restrain a breaking or a sinking of a banking, a poor subsoil, subbase course or subgrade as well as to prevent rutting or a crack of an asphalt pavement by combining belt like bodies, where fibers having flat cross section are buried in soft resin, with each other in a grid shape.

CONSTITUTION: Belt like bodies 2 composed of resin 4, in which single fibers or fiber bundles 3 having flatness of 1.5-0.8 are buried and which has hardness (Hs (JIS-A)) of 40-100 in JIS-K6301, are combined with each other in a grid shape, so that a foundation reinforcing formed body 1 can be formed. An angle θcreated between the long axis X in a cross section of these belt like bodies 2 and the long axis Y of flat fibers 3 being buried therein is set to be 0-30°. Thereby, a drawing resistance stress can be increased, and durability to crushed stones and an impact load can be heightened, and flexibility can be also secured.