PURPOSE: To improve the durability of a fan by making a motor shaft hollow and cutting the heat transmitted in the motor shaft through heat transmission by a large margin by the reduction of the heat transmission area and the air cooling from inside the motor shaft and redusing the rise of the temperature of a bearing part.

CONSTITUTION: A casing 8 is held by a stator 7 fixed onto the side surface of a case 1, and a vane 9 fixed onto a hollow motor shaft 12 is rotatably held inside the casing 8. Since the heat transmitted in the motor shaft 12 through heat transmission is cut by a large margin through the reduction of the heat transmission area and the air cooling from inside the motor shaft 12 by making the motor shaft 12 hollow, the temperature rise of a bearing 5 part can be reduced markedly. Therefore, the service life of the lubricating oil such as bearing 5 oil, grease, etc. can be prolonged by a large margin, and the durability of a combustion fan is increased, and reliability can be improved. Further, since the necessity of an auxiliary vane, etc. for cooling the motor is obviated, material cost can be reduced markedly.