An object of the present invention is to suppress the decrease in the insulation resistance between an electrode and a case resulting from condensed water in an electric heating catalyst (EHC). The EHC includes a heat generating element which generates heat by applying electricity and which heats a catalyst, a case which accommodates the heat generating element, and an insulating member which is provided between the heat generating element and the case, and which provides insulation from electricity. An electrode chamber, which is a space formed around an electrode connected to the heat generating element, is occluded by an occluding member, which has an airtightness higher than those of the heat generating element and the insulating member, in the case of the EHC.