Abstract: Provision is made for a catalyst that is arranged in an exhaust passage of an internal combustion engine and has an oxidation function, downstream side temperature detection means that detects the temperature of an exhaust gas at a downstream side from the catalyst, and addition means that adds a reducing agent into the exhaust gas from an upstream side from the catalyst, wherein there are also provided correlation value calculation means that calculates a correlation value which is correlated with an amount of change of the temperature detected by the downstream side temperature detection means when the reducing agent is added by the addition means and when a transient operation of the internal combustion engine is carried out, and determination means that determines a deterioration of the catalyst by making a comparison between the correlation value and a threshold value which indicates the deterioration of the catalyst.

Abstract: Provision is made for a catalyst that is arranged in an exhaust passage of an internal combustion engine and has an oxidation function, downstream side temperature detection means that detects the temperature of an exhaust gas at a downstream side from the catalyst, and addition means that adds a reducing agent into the exhaust gas from an upstream side from the catalyst, wherein there are also provided correlation value calculation means that calculates a correlation value which is correlated with an amount of change of the temperature detected by the downstream side temperature detection means when the reducing agent is added by the addition means and when a transient operation of the internal combustion engine is carried out, and determination means that determines a deterioration of the catalyst by making a comparison between the correlation value and a threshold value which indicates the deterioration of the catalyst.