PURPOSE: To provide a runner cavitation errosion reducing and repairing structure of hydraulic machinery that is able to securea sufficient checking effect without enlarging the form of a remolding part in the hydraulic machinery runner.

CONSTITUTION: In regard to a root part form to be composed of a flowing water surface of a runner band 5 and each runner blade surface, a tip part form of a root part at the side receiving an errosion action is reinforced by padding formation. The molding is made up into such a form that a ridgeline of a runner blade inlet tip part 4a turns its sense and it is ranged to a runner band surface, and the varying position is started from a part nearer to the runner band side below the vicinity of the center of runner inlet flow passage height, and smoothly molded so as to be ranged to the original root part form in proportion as going to the downstream side from the runner blade tip part ridgeline, and addition, an inlet curve form projected on the longitudinal section of a molded runner blade is left in status quo intact, or corrected to a form approximating to it otherwise.