To improve fuel consumption and emission, by spreading an operating region of compression self ignition combustion while avoiding knocking and unstable combustion.

This internal combustion engine of cylinder direct injection type, performing compression self ignition combustion, when it is performed, mixes fuel injected from a fuel injection valve 16 into a mixture chamber 17 provided in a two-fluid injection valve 14 with air supplied from an air pipe 19, increases aldehyde to reform the fuel into fuel enhancing ignitability by igniting the concerned mixture by a spark plug 20, and spreads an operating region of the compression self ignition combustion by injecting the concerned reformed fuel into a cylinder.