An engine-driven working machine comprising: an engine unit; a housing; and a vaned rotor; wherein the engine unit includes a crankcase, a drive-side shaft extending from a drive side of the crankcase, a magnet-side shaft extending from a magnet side of the crankcase, and oil seals (18a, 18b) sealing between the crankcase and the drive-side and magnet-side shafts (16a, 16b), wherein the housing includes a first wall, a second wall disposed adjacent to the drive side of the crankcase, and a third wall disposed adjacent to the magnet side of the crankcase, wherein the first wall is a bottom wall, and wherein the vaned rotor is a centrifugal fan fixed onto the magnet-side shaft extending beyond the third wall and disposed at a location beyond the third wall, characterized in that an air passage is defined between the crankcase and the first wall, and the air passage has an inlet opening provided in the first wall and at the same axial position as an axial position of the oil seal on the drive-side shaft so as to cause an airflow to flow along the crankcase around the oil seal on the drive side shaft, and an outlet opening provided in the third wall so as to face the vaned rotor, the outlet opening is located below the magnet-side shaft, within a right lower quarter or left lower quarter relative to the axes of the drive-side shaft and the magnet-side shaft in a circle about the axes of the drive-side shaft and the magnet-side shaft viewed from a front side, the first wall has a rib arranged near the inlet opening and extending in a direction across the drive-side shaft, and the rotations of the vaned rotor cause an airflow flowing from the inlet opening through the air passage to the outlet opening. an engine unit; a housing; and a vaned rotor; wherein the engine unit includes a crankcase, a drive-side shaft extending from a drive side of the crankcase, a magnet-side shaft extending from a magnet side of the crankcase, and oil seals (18a, 18b) sealing between the crankcase and the drive-side and magnet-side shafts (16a, 16b), wherein the housing includes a first wall, a second wall disposed adjacent to the drive side of the crankcase, and a third wall disposed adjacent to the magnet side of the crankcase, wherein the first wall is a bottom wall, and wherein the vaned rotor is a centrifugal fan fixed onto the magnet-side shaft extending beyond the third wall and disposed at a location beyond the third wall, characterized in that an air passage is defined between the crankcase and the first wall, and the air passage has an inlet opening provided in the first wall and at the same axial position as an axial position of the oil seal on the drive-side shaft so as to cause an airflow to flow along the crankcase around the oil seal on the drive side shaft, and an outlet opening provided in the third wall so as to face the vaned rotor, the outlet opening is located below the magnet-side shaft, within a right lower quarter or left lower quarter relative to the axes of the drive-side shaft and the magnet-side shaft in a circle about the axes of the drive-side shaft and the magnet-side shaft viewed from a front side, the first wall has a rib arranged near the inlet opening and extending in a direction across the drive-side shaft, and the rotations of the vaned rotor cause an airflow flowing from the inlet opening through the air passage to the outlet opening.