A selective catalytic reduction catalyst capable of reducing the NOx in exhaust gas to N2 is arranged in an exhaust pipe of an engine. Fluid feed has a fluid injecting nozzle facing the exhaust pipe on the exhaust gas upstream side from the selective catalytic reduction catalyst. The fluid feed is configured such that a urea fluid that functions as a reducing agent is fed with the selective catalytic reduction catalyst from the fluid injecting nozzle to the exhaust pipe. Ozone feed includes an ozone injecting nozzle that faces the exhaust pipe on the exhaust gas upstream side from the selective catalytic reduction catalyst, and on the exhaust gas upstream side or the exhaust gas downstream side from the fluid injecting nozzle. The ozone feed is configured such that ozone is fed from the ozone injecting nozzle to the exhaust pipe.