PURPOSE: To obtain an excellent composite reinforcing material without pretreating the material by impregnating the reinforcing material compact of inorg. short fiber, whisker, etc., with the molten metal having a specified content of group IIA element in a nitrogen atmosphere.

CONSTITUTION: The inorg. short fiber, whisker or grain or their mixture is formed into a reinforcing material compact 1. A crucible 3 contg. the compact and a matrix metal 2 contg. ≥0.4wt.% of group IIA element is set in a furnace, and the furnace is evacuated to remove oxygen. The atmosphere in the furnace is then replaced by a gaseous mixture contg. ≤3vol.% oxygen or ≤40vol.% Ar, the furnace is returned to normal pressure, the gaseous mixture ia allowed to flow through the furnace, the metal 2 is kept melted for a specified time, and then the furnace is cooled. The Al2O3, SiO2 TiO2, etc., on the surface of the reinforcing material activated by gaseous nitrogen at high temp. are reduced to metallic Al, Si, Ti, etc., by the group IIA element having a lower standard free energy of formation than the metal forming the oxide, and the wettability with the molten metal is remarkably improved.