An object of the present invention is to provide an inorganic board lighter in weight and excellent in strength and rigidity, and a method of producing the inorganic board. An inorganic board described in claim 1 for accomplishing the object comprises a hydraulic inorganic material, an inorganic lightweight material, a woody reinforcing material and a calcium silicate hydrate, wherein a ratio of the calcium silicate hydrate to the hydraulic inorganic material is 3-54 parts by mass: 100 parts by mass. Thus, by making an inorganic board, made of a hydraulic inorganic material, an inorganic lightweight material and a woody reinforcing material as main components, further contain a calcium silicate hydrate, an inorganic board which is lightweight and excellent in strength and rigidity can be obtained.