PURPOSE: To make effective use of resources by manufacturing building materials from waste paper.

CONSTITUTION: Lignin and ozone are put into contact with each other, to form ozone-oxidized lignin, and waste paper is dry-opened, to produce opened pulp raw material and, herein, three substances are mixed, i.e., those of the ozone- oxidized lignin, opened pulp raw material being 150% or more of the ozone- oxidized lignin by weight, and synthetic resin being 30% or less of the ozone- oxidized lignin by weight likewise, and the mixture is then compressed are heated in the range of 80-120°C.