An exhaust gas purification apparatus for an automotive internal combustion engine. The apparatus comprises a casing that forms a part of an exhaust gas passage of the engine. A substrate, disposed in the casing, carries a substrate to purify exhaust gas. A supporting mat is provided to support the substrate in the casing by being located between the substrate and the casing. The supporting mat has a depression to trap foreign matters at an upstream-side end of the supporting mat, the upstream-side end facing upstream side of exhaust gas flow in the exhaust gas passage.