PURPOSE: To facilitate the assembling/disassembling of a runner vane while also reduce the width of an installing space by dividing a support column which supports a discharge ring, up and down into two, and making one of the divided columns removable.

CONSTITUTION: A discharge ring 7 is horizontally divided into two. Support columns for supporting the support legs 14, 14 of the lower discharge ring 7a, can be divided up and down, and the upper stage support columns 27 are removable. When disassembling, first, the upper discharge ring is removed and suspended out. Then, the upper stage support columns 27 are removed, and the lower discharge ring 7a is lowered by that amount to get out of the way and, then, a runner vane 1 is horizontally moved and removed. An assembling operation can be carried out by reversing this procedure.