To prolong the life of a crushing tooth.

Nearly triangular crushing blades 18, 18a, and the like, are integrally protruded inside a ring part 17 and are formed thicker and thicker from the top end of the crushing blades 18, 18a, and the like, to the intermediate part 21, and thinner and thinner from the intermediate part 21 to the out edge of the ring part 17, and the intermediate part 21 having a maximum thickness is specified in width. Thereby the thickness of the intermediate part 21 easily to progress corrosion is set to be thicker than other positions, and even if corrosion occurs, the configuration of the crushing tooth 16 is maintained with the same tendency as before corrosion, and crushing can be performed by using respective positions of the teeth 16 in the same condition as before corrosion to prevent a reduction in the crushing efficiency.