To provide an ALC production process by which any reduction in strength, cracks, etc., are eliminated and ALC can be produced in a good yield, through elucidation of necessary conditions of the clay mineral content in a siliceous raw material of the ALC, in order to obtain an ALC slurry having appropriate viscosity.

This production process of ALC involves: using silica stone having a ≤15 wt.% clay mineral content as a siliceous raw material of the ALC; when the clay mineral contains chlorite-based clay mineral, using silica stone also having a ≤5 wt.% chlorite-based clay mineral content as the ALC siliceous raw material; and when silica stone having a ≥15 wt.% clay mineral content or silica stone having a ≥5 wt.% chlorite-based clay mineral content is employed, concurrently using plural kinds of silica stone, each having a different clay mineral content from those of the others, to control the clay mineral content and chlorite-based clay mineral content in the whole silica stone so as to be ≤15 wt.% and ≤5 wt.% respectively.