A joint member for a wind power generation apparatus includes: a first rotor integrally rotating with an output shaft of a speed increaser; a second rotor integrally rotating with an input shaft of a generator; and a one-way clutch provided between the first rotor and the second rotor. A torsion promoting portion being readily twisted and elastically deformed is provided at a portion of the first rotor where power is transmitted from the output shaft to the one-way clutch.