To effectively improve flame propagation speed utilizing active species in an internal combustion engine 10 that promotes combustion utilizing active species. The internal combustion engine 10 is provided with an internal combustion engine main body 11 that combusts fuel air mixture in a combustion chamber 20 and an active species generation unit 13 that generates active species in a region which a flame surface has not yet reached during flame propagation in the combustion chamber 20. In a region which the flame will eventually pass through, the active species generation unit 13 generates the active species while the flame surface has not yet reached the region.