An exhaust gas purification apparatus for an internal combustion engine comprising: a selective catalytic reduction catalyst that is arranged in an exhaust passage of the internal combustion engine, and selectively reduces NOx in an exhaust gas by using ammonia as a reducing agent; a supply device (7, 70) configured to add an additive agent, which is ammonia or a precursor of ammonia, to the exhaust gas at an upstream side of the SCR catalyst; a temperature detection device configured to detect a temperature of the SCR catalyst; and a control unit configured to increase an inflow NOx concentration which is a NOx concentration of the exhaust gas flowing into the SCR catalyst; characterized in that: the control unit is configured to, when the temperature detected by the temperature detection device (8,9) is higher than a predetermined temperature at which the NO x reduction rate of the SCR catalyst becomes a maximum, increase the inflow NOx concentration and increase an amount of addition of the additive agent in such a manner that an equivalent ratio, which is a ratio of an amount of ammonia with respect to an amount of NOx contained in the exhaust gas flowing into the SCR catalyst, becomes large, as compared to when the temperature detected by the temperature detection device (8,9) is equal to or less than the predetermined temperature. a selective catalytic reduction catalyst that is arranged in an exhaust passage of the internal combustion engine, and selectively reduces NOx in an exhaust gas by using ammonia as a reducing agent; a supply device (7, 70) configured to add an additive agent, which is ammonia or a precursor of ammonia, to the exhaust gas at an upstream side of the SCR catalyst; a temperature detection device configured to detect a temperature of the SCR catalyst; and a control unit configured to increase an inflow NOx concentration which is a NOx concentration of the exhaust gas flowing into the SCR catalyst; characterized in that: the control unit is configured to, when the temperature detected by the temperature detection device (8,9) is higher than a predetermined temperature at which the NO x reduction rate of the SCR catalyst becomes a maximum, increase the inflow NOx concentration and increase an amount of addition of the additive agent in such a manner that an equivalent ratio, which is a ratio of an amount of ammonia with respect to an amount of NOx contained in the exhaust gas flowing into the SCR catalyst, becomes large, as compared to when the temperature detected by the temperature detection device (8,9) is equal to or less than the predetermined temperature. the control unit is configured to, when the temperature detected by the temperature detection device (8,9) is higher than a predetermined temperature at which the NO x reduction rate of the SCR catalyst becomes a maximum, increase the inflow NOx concentration and increase an amount of addition of the additive agent in such a manner that an equivalent ratio, which is a ratio of an amount of ammonia with respect to an amount of NOx contained in the exhaust gas flowing into the SCR catalyst, becomes large, as compared to when the temperature detected by the temperature detection device (8,9) is equal to or less than the predetermined temperature.