To provide a machining device capable of preventing the occurrence of trouble such as the deterioration of machining quality, galling phenomena, device damage, by preventing the losing and falling of a fastening screw.

A machining device includes: a spindle; a wheel mount disposed at one end of the spindle; a machining wheel removably attached to the wheel mount and grinding or polishing a workpiece retained on a chuck table; and a machining means having a plurality of fastening screws for fixing the machining wheel to the wheel mount. Female screws are formed in the wheel mount so that a threaded portion of the fastening screw can be screwed into the female screw. This structure prevents the fastening screw from springing out of the wheel mount when the fastening screw is loosened and the machining wheel is detached from the wheel mount.