An internal combustion engine is provided that basically comprises a combustion chamber, an electric discharge unit and a controller. The combustion chamber receives a mixture of fuel and air that is caused to undergo compression self ignition. The electric discharge unit is provided inside the combustion chamber to generate an electric discharge for conducting combustion inside the combustion chamber. The controller is configured to control a voltage applied to the electric discharge unit. The controller is configured to control the electric discharge unit such that a non-thermal plasma can be formed without incurring a transition to arc discharging, and to control the quantity and distribution of an activated air-fuel mixture inside the combustion chamber in accordance with an operating condition of the internal combustion engine.