To provide a method for manufacturing an inorganic lightweight board used for soundproof (sound absorbing) boards for noise protections, inner walls of buildings, various kinds of devices which dislike the generation of sounds by the inorganic lightweight plate changed in the degree of firing of the front and the rear and the inorganic lightweight board.

At least one surface is made excessive in firing to melt part of this surface in a process step of firing an inorganic sound absorbing material. The partly molten inorganic sound absorbing material is increased in the bending strength of this portion. The strength may be improved without degrading the absorptivity of the sounds and the firing time may be shortened.