PURPOSE: To produce a lightweight and strong composite solid product excellent in the molding freedom and heat insulation by melting foamed polystyrene articles, solidifying the melted product, crushing the solidified product, kneading the obtained granular crushed product group with a cement paste, molding the kneaded product and subsequently solidifying the molded product.

CONSTITUTION: Wasted foamed polystyrene articles are melted at approximately 180-220°C, solidified and subsequently mechanically crushed into a group of the crushed products each having an irregular outline with a size of approximately ≤6mm and having a jagged and edged skin. The crushed products are homogeneously kneaded with a cement paste comprising a cement and water in a ratio of approximately 70:30. The kneaded product is injected into a mold and naturally solidified to obtain a polystyrene foam cement composite solidified product 1 having a desired shape and comprising the crushed product group 2 of the foamed polystyrene articles and the solidified layers 3 of the cement paste, the crushed products being firmly bonded to each other through the solidified layers of the cement paste.