To provide a grinding device with hardly staining grinding head and machine frame.

In this mounting structure, a fixing plate 25 and a mounting plate 11 are connected by a connecting shaft 22 at a lower end of a grinding tool spindle 8, a cup wheel type grinding tool 50 is mounted on the mounting plate 11 so that a grinding tool blade 55 provided in a ring-shape on a lower surface of a cup-shaped base body 53 may be directed downward, outer peripheries of the cup-shaped base body 53 and the mounting plate 11 are surrounded by a cylindrical grinding tool cover 28, and a mantle 31 having an annular labyrinth 30 having a reverse N-shape in cross section on an outer periphery of an upward part of the grinding tool cover 28 is provided. The annular labyrinth 30 prevents splashing of grinding liquid and grinding sludge on the surface of a substrate from scattering to the outside of the grinding head.