To provide an exhaust emission control system allowing efficient cleanup of HC and CO components and efficient supply of H2 as a reducer required for NOx reduction to a NOx cleanup catalyst.

The exhaust emission control system comprises a hydrogen generating catalyst and the NOx cleanup catalyst arranged in sequence at the upstream side of an exhaust passage for an internal combustion engine, the hydrogen generating catalyst being partitioned into a low-temperature activating catalyst part and a high-temperature activating catalyst part via the parted exhaust passage so that generated hydrogen is supplied to the NOx cleanup catalyst for reducing and cleaning nitrogen oxide. It is temporarily operated, where the internal combustion engine has an air/fuel ratio richer than a theoretical air/fuel ratio, to increase the amount of hydrogen supplied to the NOx cleanup catalyst.