PURPOSE: To shorten the manufacturing time of a windmill blade and reduce its cost by burying a metal fitting in the blade base of a main beam and screwing the main beam in a windmill main body through the metal fitting at the time of manufacture of the main beam made of fiber reinforced plastic.

CONSTITUTION: A skin 1 is formed in a blade shape made of GFRP and a main beam 2 is made of FRP or GFRP served as a reinforcement member and a windmill blade is composed of an intermediate filling material, etc., by a foaming urethane. A disc shape metal fitting 3 is buried advancely in the blade base of the main beam 2 at the time of manufacture of the main beam 2 in order to install the wind mill blade to the wind mill main body and nuts 4 for fixing are installed on this metal fitting 3 and bolts are screwed in. Thereby, as the buried metal fitting 3 is in a disc type simple shape, the manufacturing time of the wind mill blade is shortened and its workability is improved and also such defect as the unfilled up part of FRP is almost eliminated.