PURPOSE: To easily remove dust accumulated on a stay vane on an ending side of a flow in a spiral type casing.

CONSTITUTION: A hollow stay vane 7 is provided with a plurality of hollow through-holes 7a formed at a surface facing to a flow on the ending side of a flow in a spiral type casing 1, and a pipeline connected to one end of a main body, for introducing high pressure fluid. When dust is accumulated on the hollow stay vane 7, the high pressure fluid is introduced to the hollow stay vane 7, to be jetted through the through-holes 7a. Consequently, the accumulated dust can be removed. If the hollow stay vane 7 is manufactured of a steel pipe, its manufacturing cost can be reduced.