A one-way clutch structure includes: a pair of clutch members disposed between an output shaft and a drive shaft so as to oppose each other in an axial direction; and an engagement element interposed between these clutch members. When a rotation speed of the output shaft exceeds a rotation speed of the drive shaft, the engagement element engages with the clutch portion to connect the output shaft and the drive shaft so as to be integrally rotatable. When the rotation speed of the output shaft becomes lower than the rotation speed of the drive shaft, the engagement of the engagement elements is released to cut off connection between the output shaft and the drive shaft.