PURPOSE: To provide a propeller windmill simple in construction by a method wherein a propeller shaft is disposed vertically, a wind duct is provided which rotates with the propeler shaft as a center, and a bell mouth movable with the propeller as a center is supported by the wind duct.

CONSTITUTION: The main body of the windmill is composed of the propeller 1 having the vertical propeller shaft, a rotation transmitting mechanism and a generator 2. The wind duct 3 is provided so as to be rotated with the main body as a center. At a position with the propeller 1 as a center, the bell mouth 5 rotated with a support shaft 4 as a center is supported by the wind duct 3. The wind duct 3 is fitted with a tail unit 6, and a control vane 7 is linked to the tail unit 6 and the bell mouth 5. The propeller 1 is driven by winds. When the wind speed becomes higher, the control vane 7 is swung backward according to the force of the wind, moving the bell mouth 5 in an interlocked manner through the link, so that a passage for the wind is formed between the bell mouth 5 and the wind duct 3. Accordingly, the airflow is divided to limit the amount of airflow received by the propeller.