EXHAUST EMISSION CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine capable of eliminating deterioration in emission cleaning efficiency caused by deviation from true values, which is a problem inherent to integrated value control, and to save labor to reset.SOLUTION: The exhaust emission control system 25 of the internal combustion engine comprises: a catalyst 13, arranged in an exhaust path 6 of the internal combustion engine 1, for cleaning the exhaust gas; a reactant supply device 30, arranged in an upstream side of the catalyst 13, for supplying a reactant necessary for reaction with the catalytic; and a control device 24 for controlling a quantity of reactant 12 supplied by the reactant supply device 30. The control device 24 is configured to execute: a step in which a basic reactant supply quantity Ub is calculated from an operating state of the internal combustion engine 1; a step in which a correction amount Nc for the basic reactant supply quantity of Ub is calculated from the rate of change in temperature of the catalyst 13 in a transitional period; and a step in which a target quantity of reactant supply is calculated from the basic reactant supply quantity Ub and the correction quantity Nc.