To surely and with good productivity prepare a board-like inorg. molded body with specified shape, thickness and flatness without applying unnecessary forces such as bending and tension to a flexible board-like molded body immediately after dehydration and molding.

Pressurized dehydration molding of a highly water-contg. raw material 8 prepd. by mixing a calcium silicate hydrate and a polymer compd. is performed on a filter fabric 1 under a horizontal posture and the board-like inorg. molded body 8 under a flexible condition immediately after pressurized dehydration molding as it is under the horizontal posture is transferred on a belt conveyer at a synchronized speed to the filter fabric 1 by moving this filter fabric 1 and a pallet 12 for drying processing is placed on the top face and the placed pallet 12 for drying processing and the board-like inorg. molded body 8 under flexible condition are integrally rotated by 180° around a horizontal shaft center to turn over the relation of up and down position of both articles 12 and 8.