Building board

The present invention provides a building board having a flat shape in which a plurality of concave parts and convex parts are formed on a surface thereof, wherein the concave parts and the convex parts are arranged alternately and extend in the same direction, and wherein the concave parts and the convex parts are arranged such that widths thereof in a direction, in which the concave parts and the convex parts are alternately arranged, change gradually. It is preferred that the plurality of concave parts and convex parts be arranged such that the widths of the plurality of concave parts gradually increase or decrease and the widths of the plurality of convex parts gradually decrease or increase, in the direction in which the concave parts and the convex parts are alternately arranged.