Apparatus and method for purifying exhaust gas of internal combustion engine

The invention relates to an exhaust gas purifying apparatus provided with a lean NOx catalyst (3) supporting a catalyst layer, which contains a NOx trapping component, on a honeycomb substrate formed so as not to cause an alkali attack. The invention prevents trapped NOx from being dissociated and exhausted during the time of a rich spike. A NOx reducing catalyst (4) with the function of reducing NOx by a reductant in a rich or stoichiometric condition, e.g., a three-way catalyst, is disposed downstream of the lean NOx catalyst (3). In the case of increasing the amount of the NOx trapping component in the lean NOx catalyst (3) to enhance a NOx trapping capability, even if a part of trapped NOx is dissociated during the time of the rich spike, the dissociated NOx can be reduced by the NOx reducing catalyst (4) disposed on the downstream side.