A vehicle-mounted exhaust gas purifying system includes at least a first
three-way catalyst and a plurality of HC adsorbing/purifying catalysts
downstream thereof on an exhaust gas passage. Each of the HC
adsorbing/purifying catalysts includes a monolithic carrier having a
plurality of cells, and includes HC adsorbent layer and purifying
catalyst layer, which are formed on the monolithic carrier. Moreover, the
number of cells per unit areas of one HC adsorbing/purifying catalysts on
an upstream side is larger than the number of cells per unit areas of
another HC adsorbing/purifying catalyst on a downstream side.