PURPOSE: To provide a boss fixing apparatus dispensing with a shoulder portion of a shaft for a boss and does not need particular manufacturing error requirements for the length of the teeth member, and to make its assembly easy and further to prevent the biting action from becoming excessively large.

CONSTITUTION: This apparatus comprises a drive shaft having outer teeth at its end, a boss 21 having a bore having corresponding internal teeth to be inserted onto the teeth of the drive shaft, and an axial security member having a shape of a snap ring to be engaged with both annular grooves positioned at both teeth.