PURPOSE: To improve the precision and the reliability of a blade-fixing-angle changing device by detecting a blade-fixing angle of a wind power prime mover by no-contact for enabling to change the blade-fixing angle.

CONSTITUTION: A blade-fixing angle detector consists of a photoelectric distance detector 14, and fixed at ends of a fixed plate 9 and an operation shaft 6 to be used for measuring the distance to a movable plate 11 to reflect light. Since the distance is taken out as an electric signal and the detector 14 is not brought into contact with a power shaft 1 and the like, a blade-fixing-angle changing device can be obtained with high durability, reliability, and precision. Besides, a detector using supersonic wave can be similarly applied.