PURPOSE: To improve thrust by decreasing the twist of the aerodynamically active part of the blade to a specific value and succeedingly increasing to the other specific value, and decreasing the maximum relative thickness up to specific percentage.

CONSTITUTION: The twist of the aerodynamically active part of the blade 11 is decreased along the span R of the blade from about 12° on a first section where the relative span r/R is close to 45% to about 40° on a second section where the r/R is close to 0.86, and succeedingly it is increased so as to be about 4.5° at the end part section. The maximum relative camber of succesive profiles of the blade 11 is positive, it is increased from a value close to zero to about 0.04 between the r/R45% section and the end part section, and the maximum relative thickness is deceased from about 13.5% to a value close to 9.5%. In this way, excellent mechanical strength characteristic is provided, and the aerodynamic characteristic (thrust) can be improved.