To manufacture a vegetable piece forming building material composed of a vegetable piece formed into a wavy shape and having high strength and manufactured inexpensively in the mass production.

A vegetable piece forming building material is manufactured by interposing a bonding agent and a treatment chemical on a vegetable piece and forming the piece into the wave-shaped plate, or by filling of a different kind material 2 different from the vegetable piece in a recessed section at least on one side of a vegetable piece forming body S formed similarly to the above material, or by laminating a plurality of layers of vegetable piece molded bodies S and integrating them or by adding at least one plane plate 3 to the above laminate and integrating them together, or by adding at least one layer of a different kind material plate different from the vegetable piece and integrating them together or the like. The material is inexpensive and of superior strength, and as the treatment chemical is contained in the building material, the treatment is easy to contribute to the low cost. Also the treatment chemical is melted and separated, and its effect can be demonstrated semipermanently.