In order to inexpensive construction materials effectively utilizing timber resources and realizing any desired properties by using so-called low-quality materials including slim timbers, old timbers, wood cuttings produced by lumbering, bamboo, and so forth, wood, bamboo and other wooden source materials are split into fragments along their fibers by water vapor explosion, and such explosive-split fragments are shaped and hardened by adding an adhesive, mortar or expandable resin into a new wooden material such as multi-layered board, cement board or foamed resin board of explosive-split fragments. The explosive-split fragments are also usable in various fields other than fabrication of the new material.