PURPOSE: To make it possible to recycle various kinds of sludge which are industrial waste to an aggregate as various kinds of construction materials.

CONSTITUTION: Cement milk CM in the form of a slurry is mixed with the sludge S1 in the form of a slurry recovered in a quarry, etc., by a mixing section 42 and, thereafter, the resultant slurry mixture S2 is subjected to a dehydration treatment under a high pressure by a dehydrating section 43, by which cake CK is formed. The formed cake CK is then briquetted to a prescribed shape and size by the briquetting section 44 and, thereafter, the molded briquettes Ba, Bb, Bc are aged and dried and cured, by which the brequettes are recycled to the aggregate as various kinds of the construction materials.