There is provided a method for recycling synthetic wood materials, transformed into materials through a relatively simple method without performing elimination of encrusted concrete from a previously used sheathing board for use in a concrete form having synthetic wood materials as raw materials. The method consists of a step wherein a sheathing board 1 (1a) which had been previously used as a concrete form 50 and formed from synthetic wood materials with a moisture content of less than 15 wt %, wherein between 20 and 75 wt % of cellulose crushed materials, such as wood meal with particle diameters of between 50 and 200 μm, and between 25 and 80 wt % of thermoplastic resin molding materials, are mixed, is crushed into numerous coated particles 82, and a step wherein a scraping impact force is applied to each individual coated particle 82, concrete and other encrusted materials encrusted on the previously mentioned coated particles 82 are peeled or separated, and at the same time as the synthetic wood materials constituting the coated particles 82 and the encrusted materials are classified, the particles of the synthetic wood materials are granulated, and the granulated synthetic wood meal materials 83 for which the particles have been granulated are recycled.