To provide a device activating intake air for improving combustion efficiency of a displacement type internal combustion engine, reducing noxious exhaust gas such as NOx, SOx, HC and particulate matter, and improving fuel economy of the engine.

Electric discharge from an electric discharge electrode occurs by applying high frequency high voltage between the electric discharge electrode and an induction electrode, and discharged streamer which is a plasma formation source is caused. Air sent in a combustion chamber is plasma-treated by the discharge streamer to generate active species of gas contributing combustion such as O-, H+, OH-, O3, N2O, N2O5. Since these active species obtained by activation of air easily completely burn fuel, combustion efficiency is improved and noxious exhaust gas such as NOx, SOx, HC and particulate material are reduced, and fuel economy of the engine can be improved.