To provide a press die with which bending work with a bender is made possible about a metal plate on which ribs are formed and to provide a method of easily manufacturing a blade for wind power generators by utilizing the press die.

By utilizing the die (press die) 1 which consists of an upper die 10 on which a circular-arcuate convex part 11 formed at a prescribed curvature is formed along the longitudinal direction and a lower die 20 on which a circular-arcuate concave part 21 formed at a prescribed curvature is formed along the longitudinal direction and on which a plurality of grooves 22 which are deeper than the concave part 21 on this lower die 20 are formed at prescribed intervals to the longitudinal direction, the blade for the wind power generators is manufactured by applying bending work at the prescribed curvature to a metal plate 30 on which ribs 31 are formed at prescribed intervals.