PURPOSE: To increase the frequency of shift after fitting a blade once so as to prolong the time up to the time of replacement by providing a body with cavity parts extended in the axial direction of the body, then filling the cavity parts with members of high modulus of elasticity, and setting an aspect ratio, the ratio of hob tooth length to hob tooth outer diameter, to be 3 or more.

CONSTITUTION: The cylindrical face of a body 11 is provided with a tooth part 12. The form of a hob is applicable to both a solid hob and a builtup hob. The tooth part 12 is formed of the flank relief 13 of a blade tip and the cutting face 14, and the body 11 is fitted to a tool spindle through a key groove 15. The body 11 is provided with quadrangular cavities 16 extended axially, and reinforcing material 17, members higher in the modulus of elasticity than the body 11, is filled in the cavities 16. The body 11 is made of high speed steel, and an aspect ratio, the ratio of hob tooth length L0 to hob tooth outer diameter D0 is set to be 4.