PURPOSE: To prevent the elution of metals in an incineration ash and to contrive reutilizing the incineration ash as a source in a form capable of preventing environmental pollution.

CONSTITUTION: The treating method of the incineration ash is by molding and hardening the incineration ash with cement in the presence of a water soluble polymer compound. The incineration ash is compression-molded using the water soluble polymer compound having a carboxylic group or its Na salt as a molding binder in at least two steps by a compression molding machine.