A machining device includes: a spindle unit including a spindle that rotates a workpiece; and a device base having the spindle unit mounted thereon. The spindle unit includes upper and lower rolls that rotate the workpiece by contacting the workpiece, upper and lower rotary shafts that rotate integrally with the upper and lower rolls and serves as the spindle, and a support member that supports the workpiece. The device base has mounted thereon the spindle unit, a motor that rotates the upper and lower rotary shafts, and a grindstone to be brought into contact with the workpiece. The spindle unit is detachably mounted on the device base.