To provide a method for producing a sewage sludge incineration ash lightweight solidified material which has small specific gravity, higher strength in comparison with lightweight concrete and others, and high quality.

A clay-like kneaded material 1 containing a large amount of bubbles is prepared by a method in which sewage sludge incineration ash added with a polymer flocculant, an acid solution, and a foaming agent are mixed/ kneaded. The material 1 is molded and solidified by drying naturally, or a prescribed amount of the material 1 is put into a form 2, heated, expanded, and solidified. A kind of powder which generates gas by water or an dilute acid such as sodium hydrogen carbonate, powdered aluminum, and powdered iron is used as the foaming agent.