The electricity is suppressed from flowing through a case (5) of an electric heating catalyst (1). The electric heating catalyst (1) comprises a heat generating element (3) which generates heat by applying electricity; a case (5) which accommodates the heat generating element (3); an inner tube (4) which is provided between the heat generating element (3) and the case (5); a mat (6) which is provided between the heat generating element (3) and the inner tube (4) and between the inner tube (4) and the case (5) and which insulates the electricity; and an electrode (7) which is connected to the heat generating element (3) and which supplies an electric power to the heat generating element (3); wherein an insulating layer (41), which insulates the electricity, is formed on a surface of the inner tube (4); and the insulating layer (41) is formed so that a portion, which is disposed on an inner circumferential surface side (403), is thinner than a portion which is disposed on an outer circumferential surface side (402) of the inner tube.