An electrically heated catalytic converter for purifying exhaust gas, the electrically heated catalytic converter comprising: a catalyst carrier supporting a catalyst and configured to generate heat by energization; a case for accommodating the catalyst carrier; and an electrical insulation mat interposed between the catalyst carrier and the case, wherein the case comprises an outer tube disposed at the outermost side and an inner tube disposed inside the outer tube; the inner tube has a portion where the radius of the inner tube decreases toward the upstream side, in a cross section upstream of the catalyst carrier taken along a plane including the central axis of the case, the portion where the radius of the inner tube decreases toward the upstream side consists of a first curved portion and a second curved portion formed in this order from the side closer to the catalyst carrier, the first curved portion is curved so as to outwardly project and the second curved portion is curved in the direction opposite to the curvature of the first curved portion so as to project toward the central axis, the second curved portion has a curvature radius larger than that of the first curved portion, and an insulation layer is formed on at least the first curved portion of the inside of the inner tube and other portions of the inside of the inner tube, characterized in that the thickness of the insulation layer in the first curved portion is equal to or greater than one time to less than 1.4 times the thickness of the insulation layer on other portions, the curvature radius of the first curved portion is 5 to 15 mm, and the curvature radius of the second curved portion is 40 to 50 mm. a catalyst carrier supporting a catalyst and configured to generate heat by energization; a case for accommodating the catalyst carrier; and an electrical insulation mat interposed between the catalyst carrier and the case, wherein the case comprises an outer tube disposed at the outermost side and an inner tube disposed inside the outer tube; the inner tube has a portion where the radius of the inner tube decreases toward the upstream side, in a cross section upstream of the catalyst carrier taken along a plane including the central axis of the case, the portion where the radius of the inner tube decreases toward the upstream side consists of a first curved portion and a second curved portion formed in this order from the side closer to the catalyst carrier, the first curved portion is curved so as to outwardly project and the second curved portion is curved in the direction opposite to the curvature of the first curved portion so as to project toward the central axis, the second curved portion has a curvature radius larger than that of the first curved portion, and an insulation layer is formed on at least the first curved portion of the inside of the inner tube and other portions of the inside of the inner tube, characterized in that the thickness of the insulation layer in the first curved portion is equal to or greater than one time to less than 1.4 times the thickness of the insulation layer on other portions, the curvature radius of the first curved portion is 5 to 15 mm, and the curvature radius of the second curved portion is 40 to 50 mm.