To efficiently perform replacement of a rotary grinding wheel.

In a grinding device 1 to eliminate flaws by polishing the surface of a slab 20, a chamber 5 is formed in a gate-shaped frame, and a polishing mechanism 6 is contained. The grinding device 1 is movable on a rail 4 provided on a factory floor surface 3 along length of the slab 20, and a heat-proofing plate 16 is provided on a floor surface of the chamber 5, except for an aperture part 17 above the slab 20. Close to the slab 20, a rack 23 to contain plural grinding wheels 22 for replacement is disposed, so as the device 1 moves to above the rack 23, with a door 18 provided on the heat-proofing plate 16 opened, the grinding wheel 22 can be replaced between that and the rack 23.