A degree of dispersion of a reducing agent added to an exhaust gas flowing into an exhaust gas purification apparatus is controlled. Before addition fuel is added, a valve opening Vd of a flow area changing valve is changed to generate pulsation of the exhaust gas, so that addition valve vicinity exhaust gas pressure Pg varies periodically. Addition timing TMad is controlled to synchronize with extremum arrival timing TMe. High or low dispersion type addition control adds fuel at timing (CP) when the addition valve vicinity exhaust gas pressure Pg becomes a maximum value Pgmax, at timing (TP) when at a minimum value Pgmin, or at both timings (CP, TP).