PURPOSE: To obtain the least water-stream loss and improve the efficiency of a rotary hydraulic machinery by successively reducing the plate thickness of the outer periphery side back surface of a stay vane in taper form to the outer periphery side end surface.

CONSTITUTION: The plate thickness T on the back surface 4B side of a stay vane 4 is cut in taper form from an arbitrary position to the outer periphery end surface 4E along the direction from the inner periphery end surface on the guide vane side to the outer periphery end surface 4E of the vortex casing, and a part of the back surface 4B is formed as a tilting surface 4C When the tilting surface 4C is formed on the back surface 4B of the stay vane 4, the inlet angle reduces to αB. When the inlet angle dB is made nearly equal to the exit angle α2 after cutting, the shape of the stay vane corresponds to the shape of the free vortex, and the band conditions such as increase of the diameter of the vortex casing and reduction of the distance between stay vanes can be avoided.