To stably store an accumulated material made by laminating many sheets of thin wet veneers obtained by slicing a flitch made by laminating a raw material for a long time without generating discoloration of a water stain and the like around.

After coating a solution of a surface active agent or sprinkling water onto an exposed surface of the accumulated material made by laminating many thin set veneers of about 0.2 to 0.3 mm thickness, the accumulated material is stored in the same way as conventional. Condensation can be prevented from being formed with the surface active agent and water stains is not generated.