PURPOSE: To provide an engine room structure which can prevent heat from returning again to a radiator by enhancing the ventilator efficiency of the inside of an engine room so as to obtain a satisfactory temperature distribution condition.

CONSTITUTION: A radiator 13 for carrying out heat-exchange with the ambient air, is disposed, and an engine 14 having an exhaust manifold 15 at the front surface 14a thereof is disposed downstream of the radiator 13. A duct 18 is extended from the periphery of the radiator 13 to the front surface 14a including the exhaust manifold 15, and is prolonged to a position in rear of the engine 14 so that its rear end opening 18f facing an air outlet opening 12a of an engine room 12. Further, a fan is provided for introducing the ambient air into the duct 18 through the radiator 13, and discharging the same from the rear end opening 18f.