In order to provide a method of molding plant-based material to mold three-dimensional shape of cross section for relatively long plant-based material while maintaining the continuity of original cell/tissue of the plant-based material by means of simple equipment and process, we obtained a long plant-based material of high density and high strength by continuously giving compressing/drawing deformation to the component tissue of the plant-based material toward the center direction while extruding the plant-based material via the extruding die having a prescribed extrusion ratio and die angle for a relatively long plant-based material long in the fiber direction.