In a pre-process, a particle shape substance is decomposed and removed using a cyclone and an electric dust collection apparatus, NOx in an exhaust gas is decomposed completely using discharge, to establish technique for generating NO2 for necessary to oxidize a particle shape substance in a real time. The generated NO2 and ozone and active oxygen generated the particle shape substance is decomposed completely. NO2 for necessary to the particle shape substance is generated and is processed in response to operation condition of an engine.