An engine-driven work machine is provided in which an engine/work machine unit (5) is housed in a box (30) and a cooling fan (15) for generating a flow of cooling air from an air inlet (39) to an air outlet (40) via the surroundings of the engine/work machine unit (5) is disposed within the box (30), wherein a gas/liquid separation chamber (32) for restricting the flow of cooling air is provided between the air inlet (39) and the engine/work machine unit (5), and the gas/liquid separation chamber (32) is provided with a first wall face (32a1) for changing upward flow of cooling air into a lateral direction after it has collided with the first wall face (32a1) and a second wall face (32a2) for changing the lateral direction of flow into an obliquely downward direction. This enables mist contained in cooling air taken into the box to be separated and removed effectively before the cooling air reaches the surroundings of the engine/generator unit.