To materialize a control technique in a spark ignition engine 100 by which a mixed status of fuel/air mixture can be made appropriately with respect to each combustion while switching between stratified combustion and homogeneous combustion in accordance with load.

In the spark ignition engine, an intake port 10 is partitioned by a partition wall 12 into a first port 15 positioned outside to the midsection and a second port 16 positioned on a side closer to the midsection than the first port 15, and provided with a port switching means 35 for freely switching between a first state in which the second port is closed while opening the first port 15 and a second state in which the second port is opened while closing the first port. In a fuel supply means 30, fuel G is supplied to the midsection of a combustion chamber 1 from the supply part 14a disposed on a side closer to the midsection than the second port 16.

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