PURPOSE: To manufacture an ALC molded product having no cavities without the cutting or turning process by setting a form with almost closed cavity in a manner that its longitudinal direction is inclined to the horizontal direction at the specified angle and that the overall height is not beyond the specified length, and then casting light aerated concrete (ALC) raw material slurry into the cavity.

CONSTITUTION: A form 3 is so set that is longitudinal direction is inclined in the range of 5 - 85°C, preferably 30 - 60°C and that its overall height is not beyond 3,000mm. Subsequently, ALC raw material slurry 27 is cast from a casting component 19 provided on the upper end of the form 3 and a casting inlet 18 into both cavities 14 and 15 to foam and solidify to form uncured molded materials 28 and 29. At that time, if the cavities 14 and 15 are almost closed, the form 3 is inclined by 5°C or more in the horizontal direction and surplus foams are released upward to eliminate the generation of cavities.