An inorganic board contains, in a solid content ratio, 30 to 70 mass % of hydraulic material, 5 to 15 mass % of reinforcing fiber, and 1 to 30 mass % of wollastonite having a wet volume (after being allowed to stand for 30 minutes) of 15 to 45 ml. Also, a method includes: step of producing a slurry containing hydraulic material, reinforcing fiber, and wollastonite; step of producing a sheet by dehydrating the slurry; and step of pressing and curing the sheet; wherein, in the step of producing a slurry, a composition of the slurry is set so as to contain, in a solid content ratio, 30 to 70 mass % of hydraulic material, 5 to 15 mass % of reinforcing fiber, and 1 to 30 mass % of wollastonite having a wet volume (after being allowed to stand for 30 minutes) of 15 to 45 ml.