Provided is a functional building board having an antimicrobial function,
which retains anti-algal and antifungal agents for a long period of time
in a coat on an external wall material by using several kinds of
antimicrobial composite materials, and is provided with stain-proofing
function to wash away stains on the external wall material, and in which
the design is not largely restricted by the color of the anti-algal or
antifungal paint or by the state of the coat and the design is not
influenced by the coating step in the final step.The building board
according to the present invention has a coat formed on the surface, and
is characterized in that antimicrobial composite materials are included
on the surface of the coat and a coat layer containing colloidal silica
as a main component is formed, said antimicrobial composite materials
being characterized in that they control generation of algae and fungi
and said building board being a fiber reinforced cement board.