A sintered porous metal filter permitting passage of gases therethrough includes a filter portion having specified pores for trapping and separatin dust from the gas to be treated, and a support portion for supporting the filter portion. The support portion has pores greater than the pores of the filter portion to diminish the pressure loss of the gas to be treated. The filter portion includes metal particles of small diameter, and the support portion includes metal particles having a greater diameter than the filter portion forming metal particles. The filter portion and the support portion are formed by sintering the two kinds of metal particles by hot isostatic pressing to provide an outer side and an inner side integrally. A catalyst reaction portion is formed in the filter portion or the support portion, or as an independent catalyst layer to make noxious components of the gas harmless.