A construction machine includes a front working implement operable as a result of driving of an engine, a urea SCR catalyst arranged in an exhaust gas line from the engine to purify and reduce nitrogen oxides in exhaust gas, an aqueous urea solution tank for storing an aqueous urea solution, a temperature detector for detecting a temperature of the aqueous urea solution, an air conditioner for air-conditioning an operator's cab, and a warm/cold air guiding device for guiding warm/cold air, which has been blown out of the air conditioner, to the aqueous urea solution tank in accordance with the temperature of the aqueous urea solution. The warm/cold air guiding device includes a controller for outputting a warm air control signal or cold air control signal, which corresponds to a temperature of the warm/cold air blown out of the air conditioner.