To provide an internal combustion engine controlling an air flow in order to set an exhaust gas temperature at which the exhaust gas is reformed according to an air flow condition, and optimally reforming exhaust gas.

This internal combustion engine includes an alcohol concentration detection step (step S11) of detecting an alcohol concentration in fuel, a step (step S12) of determining the presence or absence of abnormality of a reforming catalyst, a step (step S13) of determining respective areas of air flow areas A, B, C and D according to the alcohol concentration detected in step S11 when the reforming catalyst is normal, and a step (step S14) of switching to a map representing distribution of the air flow areas A, B, C and D with respective air flow areas determined in step S13. The air flow areas A, B, C and D are determined according to the presence or absence of abnormality of the reforming catalyst and the alcohol concentration, and strength and weakness of the air flow is determined, thereby controlling the air flow in order to set the exhaust temperature at which the exhaust gas is reformed according to the air flow condition and efficiently reforming the exhaust gas.