PURPOSE: To make a pad installable in a pad mounting disk without stopping a rotating spindle at the home position at the time of pad changing by installing a guideway, moving a mounter body centripetally to an eccentric center of the pad mounting disk with the lifting of a pad unit body, on top of the mounter body.

CONSTITUTION: A lower end of a lifting cylinder 43 is attached to a mounting base 33 via a universal joint 39, and a mounter body 53, mounting a circular abrasive pad 22, is clamped to the tip of a piston rod of this lifting cylinder 43. A guideway 55, being guided to a magic fastener 31 of a pad mounting disk 16 by lifting motion of the mounter body 53, while this body 53 is horizontally moved centripetally to an eccentric center Q of the pad mounting disk 16, is installed in an inner circumferential surface of a cylinder part 54 of this mounter body 53. With this constitution, the pad 22 is installable in the pad mounter disk 16 without stopping a rotating spindle at the home position at the time of replacement of the circular abrasive pad 22.