PURPOSE: To secure strength and rigidity simultaneously by constituting a blade side plate in a way of unifying light metal constituent member, being solidly formed with a blade and of the same time material of the blade, with a ferrous metal constituent member as one body.

CONSTITUTION: A blade 1 is made of light metal of less than 4 in specific gravity such as Al(Al alloy), Mg(Mg alloy), or the like, and a light metal constituent member 21 of the same material with this blade 1 and a ferrous metal (carbon steel, stainless steel or the like) constituent member 22 are unified as one body, through which a blade side plate 4 is constituted. This light metal constituent member 21 is solidly formed with the blade 1 by way of casting, forging processes and so on. It is necessary that the light metal constituent member 21 and the ferrous metal constituent member 22 are firmly coupled as one body even in a high temperature state, and a linear expansion factor of the ferrous metal constituent member 22 is desired to be approximated to that of the light metal constituent member 21. With this constitution, strength and rigidity in the blade side palte 4 are thus securable.