To easily remove a motor under a state wherein the main body in being attached to an attic space.

For this ventilation fan, a casing 30 is attached in a main body 20 of which the lower surface is open. Then, a motor 52 is attached to a motor attaching base 51 to form a motor unit 50, and a fan 40 is connected to the output shaft of the motor 52. A fan insertion hole 36 is formed on a motor attaching plate 35 of the casing 30, and the fan 40 is inserted in the casing 30 through the fan insertion hole 36. At the same time, the motor attaching base 51 is fixed to the motor attaching plate 35 with bolts 44, and a lower surface cover 60 is attached to the lower section of the main body 20 with bolts 61. By this constitution, the fan 40 and the motor unit 50 can be removed from the main body 20 removing the lower surface cover 60 and loosening the bolts 44, and the motor 52 can be easily removed from the main body 20 under a state wherein the main body 20 is being attached to an attic space.