A power apparatus including a reducing agent supply control system according to an embodiment of the present invention comprises: an engine for combusting air and fuel with a predetermined air-fuel ratio and discharging exhaust gas containing nitrogen oxides; an exhaust flow path along which the exhaust gas discharged from the engine moves; a pressure sensor for measuring the actual pressure of air supplied to the engine; a nitrogen oxide concentration sensor which is installed on the exhaust flow path so as to measure the concentration of nitrogen oxides in the exhaust gas; a reducing agent supply unit for supplying a reducing agent to the exhaust gas which moves along the exhaust flow path; and a control unit for determining the quantity of the reducing agent on the basis of informationreceived from the pressure sensor and the nitrogen oxide concentration sensor, so as to control the reducing agent supply unit.