To enable a device to automatically replace a polishing tool.

In a polishing device mounting a polishing tool 35 in a spindle in an arm of a robot, while pressing the polishing tool 35 to a polished surface of a metal mold run along it, and polishing the polished surface, a T-shaped holder 30 is provided in a tip end part of the spindle, in the polishing tool 35, a pair of notches press fit engaging a pair of lock pins 33 of the T-shaped holder 30 and permitting unreasonable extraction are provided, in the vicinity of a metal mold placing area, a tool storage space (base) 41 arranging a plurality of the polishing tools 35 and a tool detaching base 45 formed with a narrow width horizontal slit 47 enabling the lock pin 33 to pass are provided, an arm (holder 30) is made to rise so that the lock pin 33 passes through upward the slit 47 of the tool detaching base 45, after the polishing tool 35 is detached from the holder 30, the arm (holder 30) is lowered down from upward of the polishing tool 35 in the tool storage space, so as to install the polishing tool 35 in the holder 30, the polishing tool can be automatically replaced.