PURPOSE: To prevent the melt deterioration of fiber in the above cement plate by providing a first process of carrying out the autoclave curing of a plate- shaped cement body, a second process of carrying out the water curing of the same for a predetermined period or longer, and a third process of drying the same so as to reduce the water content of the same to a fixed ratio or below in the range of specific temperatures.

CONSTITUTION: A polypropylene fiber, a polyethylene fiber and a polyvinyl alcohol fiber, which are thermoplastic synthetic resin fibers, are used as a synthetic resin fiber to be added to a cement plate. Autoclave curing in a first process is set to 1 to 3 atm G, and heat at the time of this curing is lowered as much as possible to prevent the heat deterioration of the synthetic resin fiber and to enhance the bonding strength of a cement matrix. A water curing period in a second process is set to 15 days or longer to promote the hardening reaction of cement. Drying in a third process is carried out for removing surplus water contained in the cement plate by the water curing, and a drying temperature is limited to 80 to 110°C to reduce a water content in the cement plate to 2% or less.