Abstract: In order to suppress ammonia from flowing out during regeneration treatment of a filter carrying an SCR catalyst, the prevent invention provides an exhaust emission control system, of an internal combustion engine, including a first stage catalyst having an oxidation function, a fuel supply device configured to supply fuel to the first stage catalyst, a filter provided in the exhaust passage downstream of the first stage catalyst and carrying a selective redaction type NOx catalyst, an ammonia supply device configured to supply ammonia to the filter, a filter-regeneration-treatment executing unit configured to execute filter regeneration treatment, and a control unit configured to supply, when the filter regeneration treatment is not executed, the ammonia in an amount corresponding to an amount of the NOx emitted from the internal combustion engine, and to supply, when the filter regeneration treatment is executed, the ammonia in an amount corresponding to an amount of the NOx obtained by subtracting, from th