The object of the present invention is to provide an inorganic board which has high mechanical strength, much improved dimensional stability, freezing and fusion resistance. To attain said object, the present invention provides an inorganic board made of a cured material being a raw material mixture containing a cementitious inorganic material, a silica containing material, a woody reinforcement, and a water soluble synthetic resin, wherein the mass ratio of said cementitious inorganic material and said silica containing material is set to be in the range of between 35:65 and 45:55, to promote the hardening reaction of said inorganic board, and to reduce the unreacted materials, solving the problem of the retardation of the cement hardening by said water soluble synthetic resin.