PURPOSE: To perform self starting operation for a high speed windmill and simplify its construction, by mounting a low speed windmill body of vertical shaft type with its rotary shaft in common to the inside of a high speed windmill body of vertical shaft type.

CONSTITUTION: To the inside of a high speed windmill body 2 of vertical shaft type, a Savonius low speed windmill body 3 of vertical shaft type is mounted with a rotary shaft 2A in common. The low speed windmill body 3, in which if speed of a wind is constant the lower is the rotary speed the larger is rotary torque, is used as a starting windmill, and in case of high rotary speed when the high speed windmill body 2 is in operation of generating power the low speed windmill body 3 produces auxiliary power. In this way, self starting operation is capable to eliminate the necessity for using a starting motor, power source and controller, thus the construction can be simplified.