To provide an internal combustion engine capable of executing the optimum modification and the deterioration recovery of the modification catalyst by judging whether or not a modification catalyst is deteriorated for enabling judgment on the deterioration of the modification catalyst in an early stage, and determining the deterioration factor for enabling selection of a recovery method according to the deterioration factor.

The internal combustion engine judges the deterioration speed of a modification catalyst in the case the proportion of gasoline in a fuel judged by a fuel property sensor is the same as or higher than a predetermined value, or it determines the sulfur content of the modification catalyst based on the ratio of the deterioration speed of the modification catalyst and a reference speed of the reference value in the case the deterioration speed is the same as or higher than a reference value of the deterioration speed of the modification catalyst in a predetermined time provided in advance. Thereby, the fuel jetting amount and recovery amount are determined from the engine conditions, the fuel gasoline proportion, and the sulfur content of the modification catalyst so that the modification efficiency of the modification catalyst is improved in an early stage by judging deterioration of the modification catalyst by the sulfur content in an early stage.

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