To efficiently create reformed gas while performing lean operation.

This internal combustion engine is provided with at least one first combustion pattern cylinder 1b, 1c performing first combustion pattern, at least one second combustion pattern cylinder 1a, 1d performing second combustion pattern, an exhaust gas route 3 discharging exhaust gas from the first and the second combustion pattern cylinders 1a-1d to outside, an exhaust gas branch route 13 branching at least part of exhaust gas from the second combustion pattern cylinders 1a, 1d, a fuel supply device 14 supplying fuel in the exhaust gas branching route 13, a reformer 12 creating reformed gas from exhaust gas in the exhaust gas branch route 13 and fuel supplied in the exhaust gas, a reformed gas introduction route 15 introducing reformed gas to the intake air route 2, and a control device 4 injecting fuel from the fuel supply device 14 to perform lean combustion in the first combustion pattern cylinders 1b, 1c and rich combustion or stoichiometric combustion in the second combustion pattern cylinder 1a, 1d.

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