To provide a noxiousness removing method for a used incinerating facility to be demolished for making noxious substance such as dioxin contaminating inner wall surfaces of the incinerating facility such as an incinerator, a flue, and a stacks harmless, so that it can be demolished by a general demolition method, and a noxiousness removing method for castable of an incinerator in maintenance work, to allow safe maintenance work to be conducted without contaminating work environments.

Opening parts of the flue 5 of the incinerator, the stack or the like contaminated with noxious substance such as dioxin are closed with closing covers 7 and 7A. Diluted liquid of high density silicate solution diluted with special dispersion liquid is sprayed to an inner wall 8 of the flue, so that noxious substance such as incineration ash and soot attached to the surface of the inner wall 8 of the flue penetrates into micro-pores and cracks in the inner wall 8 of the flue, and the inner wall 8 of the flue is then heated by a combustion burner 17.