To provide a replaceable blade in which the problems of conventional blades wherein, though a multivane blade generating power even with weak wind is most suitable for small-sized wind power generators, the entire part of the windmill may be damaged in a strong wind and the safety is difficult to maintain since its number of blades is large, and it is not suitable for wind power generators since the rotational speed of the blades is small and manufacturing cost is high are remarkably improved.

This blade is composed of main blades 1 rotating a windmill and a base blade 2 having a strength at the root parts and to which base blades 2 are fitted. Within a predetermined allowable limit, the main blades 1 are replaceable according to a power generation amount without being limited by the size and material of the blades. The blades 1 can be increased in size by mounting struts to secure safety. Most parts can be commonized without changing the entire part of the wind power generator. The blade has such a structure that can remarkably reduce cost, and increase a power generation efficiency by increasing or decreasing the rotational speed of a shaft.