PURPOSE: To facilitate the manufacture of a rectangular bamboo board through the cutting of the round bamboo material and extend the application for the building and floor material by rectangularly cutting a bamboo piece made by vertically cutting bamboo material to the elongated direction.

CONSTITUTION: A bamboo material 1 is cut to form a plurality of vertically cut pieces 2. A bamboo whose stem hypodamic portion is thick is preferably used for bamboo material 1. The vertically cut pieces 2 are rectangularly cut to form a bamboo board. It is advisable from the yield rate viewpoint that when rectangularly cutting the bamboo material, the long side thereof is in contact with the inner circumference of the bamboo material 1 so that the external skin may not remain on the bamboo board 4 since the vertically cut piece 2 is bent like an arc. The surface of the bamboo board 4 is ground and finished to remove the outer skin because said skin becomes discolored with elapse of time. Since the bamboo board 4 is made of hypodamic portion with many vascular bundles, it has strength, fragility-resistance, bend-resistance, corruption-resistance, durability and waterproof characteristics.