Abstract: The control device displaces the main shaft in the axial direction and in the radial direction within the range of the gap between the rib member of the main shaft and the axial magnetic bearing and the gap between the main shaft and the radial magnetic bearings, by controlling the attraction forces of the axial electromagnets and the radial electromagnets, whereby the main shaft can be positioned. By controlling the axial magnetic. bearing and the radial magnetic bearings, it becomes possible to freely displace only the main shaft in the axial direction and in the radial direction, and therefore, the main shaft can be positioned at high speed and with high precision. Moreover, there is no necessity of providing the feeding mechanism in which the ball screw mechanism and linear motor etc. are employed for the purpose of displacing the magnetic bearing spindle device, and hence, reduction of the production cost for the grinding apparatus can be achieved.