An exhaust emission control system of an internal combustion engine, comprising: a first stage catalyst provided in an exhaust passage of an internal combustion engine and 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 configured to collect particulate matter in exhaust gas, the filter carrying a selective reduction type NOx catalyst that reduces NOx in the exhaust gas using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or a precursor of the ammonia to the filter; a filter-regeneration-treatment executing unit configured to execute filter regeneration treatment for supplying the fuel from the fuel supply device to the first stage catalyst to raise temperature of the filter to a predetermined filter regeneration temperature, at which oxidation of the particulate matter is facilitated, to thereby oxidize and remove the particulate matter deposited on the filter; and a control unit characterised in that said control unit is to supply, when the filter regeneration treatment is not executed, the ammonia or the precursor of the ammonia in an amount corresponding to an amount of the NOx emitted from the internal combustion engine using the ammonia supply device, and to supply, when the filter regeneration treatment is executed, the ammonia or the precursor of the ammonia in an amount corresponding to an amount of the NOx obtained by subtracting, from the amount of the NOx emitted from the internal combustion engine, an amount of the NOx reduced by the fuel which is supplied by the fuel supply device and passes through the first stage catalyst. a first stage catalyst provided in an exhaust passage of an internal combustion engine and 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 configured to collect particulate matter in exhaust gas, the filter carrying a selective reduction type NOx catalyst that reduces NOx in the exhaust gas using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or a precursor of the ammonia to the filter; a filter-regeneration-treatment executing unit configured to execute filter regeneration treatment for supplying the fuel from the fuel supply device to the first stage catalyst to raise temperature of the filter to a predetermined filter regeneration temperature, at which oxidation of the particulate matter is facilitated, to thereby oxidize and remove the particulate matter deposited on the filter; and a control unit characterised in that said control unit is to supply, when the filter regeneration treatment is not executed, the ammonia or the precursor of the ammonia in an amount corresponding to an amount of the NOx emitted from the internal combustion engine using the ammonia supply device, and to supply, when the filter regeneration treatment is executed, the ammonia or the precursor of the ammonia in an amount corresponding to an amount of the NOx obtained by subtracting, from the amount of the NOx emitted from the internal combustion engine, an amount of the NOx reduced by the fuel which is supplied by the fuel supply device and passes through the first stage catalyst.