An exhaust gas treatment system for an internal combustion engine includes an exhaust pipe (6) and an energy applying device (12). Exhaust gas discharged from the internal combustion engine flows into the exhaust pipe (6). The energy applying device (12) applies energy to the exhaust gas flowing through the exhaust pipe. The energy applied to the exhaust gas is greater than the energy for decomposing nitrogen monoxide (NO) and less than the energy for decomposing nitrogen (N 2 ).