PURPOSE: To improve the cavitation characteristic at the outlet of outercircumference of runner vane by providing a recess for suppressing leakage of water from high to low pressure face side along the vane profile in the outercircumferential end face of runner vane.

CONSTITUTION: An elongated recess 12 is made longitudinally in the outercircumferential face of runner vane 11 while predetermined gap is maintained between the outercircumferential face of runner vane and discharge ring 3. The leak flow S flowing along the high pressure face side 11a of runner vane will drop the pressure through increase of flow path resistance caused by the recess 12 made in the outercircumferential end face of runner vane to suppress leakage to the low pressure face side 11b. Consequently, the turbine efficiency is improved to suppress cavitation at the outlet of outercircumference of runner vane.