An exhaust purification device for an engine , the exhaust purification device comprising: a selective reduction catalytic converter that is provided in an exhaust path of the engine , and selectively reduces and purifies nitrogen oxide in exhaust by using a reducing agent; an injection device that injects and supplies a liquid reducing agent or a precursor thereof to an upstream portion of the selective reduction catalytic converter ; a tank that stores the liquid reducing agent or the precursor thereof, the liquid reducing agent or the precursor thereof being to be injected and supplied from the injection device ; a reducing agent supply flow path (250; 251) that supplies the liquid reducing agent or the precursor thereof from the tank to the injection nozzle ; a reducing agent circulation flow path that is branched from the reducing agent supply flow path (250; 251), is capable of returning a part of the liquid reducing agent or the precursor thereof to the tank , and has a part disposed to be capable of exchanging heat with a heat source; a reducing agent circulation valve that controls a flow of the liquid reducing agent or the precursor thereof to the reducing agent circulation flow path ; a temperature detection unit that detects a temperature of the liquid reducing agent or the precursor thereof in the tank or the reducing agent supply flow path (250; 251); and characterized in that said exhaust purification device further comprises: a reducing agent circulation control unit that controls the reducing agent circulation valve by outputting a control signal to an actuator that controls the reducing agent circulation valve so that the liquid reducing agent or the precursor thereof can flow into the reducing agent circulation flow path when the temperature of the liquid reducing agent or the precursor thereof is equal to or less than a predetermined temperature, the temperature being detected by the temperature detection unit . a selective reduction catalytic converter that is provided in an exhaust path of the engine , and selectively reduces and purifies nitrogen oxide in exhaust by using a reducing agent; an injection device that injects and supplies a liquid reducing agent or a precursor thereof to an upstream portion of the selective reduction catalytic converter ; a tank that stores the liquid reducing agent or the precursor thereof, the liquid reducing agent or the precursor thereof being to be injected and supplied from the injection device ; a reducing agent supply flow path (250; 251) that supplies the liquid reducing agent or the precursor thereof from the tank to the injection nozzle ; a reducing agent circulation flow path that is branched from the reducing agent supply flow path (250; 251), is capable of returning a part of the liquid reducing agent or the precursor thereof to the tank , and has a part disposed to be capable of exchanging heat with a heat source; a reducing agent circulation valve that controls a flow of the liquid reducing agent or the precursor thereof to the reducing agent circulation flow path ; a temperature detection unit that detects a temperature of the liquid reducing agent or the precursor thereof in the tank or the reducing agent supply flow path (250; 251); and <EOS>