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 sealing between the crankcase and the drive-side and magnet-side shafts , 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 sealing between the crankcase and the drive-side and magnet-side shafts , 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 . <EOS>