To provide a panel board wherein a bamboo material being a bamboo material treated product having reality is used as a core by considering that a circular section is a reason for disturbing service conveniences of the bamboo material and thinking out a measure for making treatment in the next process easy as a building material.

A treated bamboo material 1 wherein reference surfaces 12 are oppositely formed by removing opposed two surfaces is manufactured so that bamboo material not yet treated has a constant thickness in its longitudinal direction. By one piece of the bamboo material 1 or by lining up a plurality of treated bamboo materials 1 so that the reference surfaces 12 face to the same direction, core bodies 15 are formed, and a front shell material of a front shell board 2 and the like is stretched to either one side or both sides of the respectively opposed reference surfaces 12 of the core body 15.