PURPOSE: To enhance accuracy in finish work by allowing machining on the entire peripheral face of a rotor hub including the top face thereof.

CONSTITUTION: The rotor hub machining unit performs cutting on a covered cylindrical hub supported rotatably on a fixed shaft through bearings with a recording disc being loaded on the outer periphery thereof. A motor shaft 2 has one end supported coaxially with a fixed shaft 5 by a supporting part 6 provided at the tip thereof and the other end supported by a center shaft 17 movable in the axial direction, and an axial sliding body 9 is provided on the outer periphery of the fixed shaft 5. A rotary body 12 is provided rotatably on the outer periphery of the sliding body 9. A press body 13 provided with a rubber member 14 is secured to the bottom end face of the rotor hub 3 which is then rotated through the press body 13 upon rotation of the rotary body 12 thus moving a tool and cutting the peripheral face of the rotor hub 3.