To provide a method for manufacturing agglomerate matter and pellets of a lightweight composite resin of high strength, obtained by adding eject such as shirasu, pumice, fallen pumice or the like to a ground material of various wastic plastics to knead the same with the ground material, and using the same to produce a lightweight molded processed article of high strength.

The agglomerate and pellets (1) of the lightweight composite resin of high strength are obtained by adding particles of the eject (glass element-containing matter) to the ground material of various waste plastics to knead the same with the ground material under heating. The substitute article (2) of the lightweight concrete processed secondary product of high strength is manufactured by the molding processing of the agglomerate matter or pellets of the lightweight composite resin of high strength. The product obtained by this manufacturing method is also disclosed.