Abstract: A grinder including a power drive unit having a driving shaft and a bevel gear fixedly mounted on one end of the driving shaft, and a grinding unit coupled to the power drive unit, the grinding unit including a grinding bit and a transmission mechanism coupled between the grinding bit and the bevel gear of the power drive unit, wherein the grinding unit has a retaining hole and a coupling flange disposed at a rear side thereof at different elevations; the power drive unit has a front coupling slot at a bottom side thereof which receives the coupling flange of the grinding unit, a pair of lugs raised from the periphery at a top side thereof, a lever pivoted to the lugs, and a hook pivoted to the lever and forced by the lever to hook in the retaining hole of the grinding unit. The transmission mechanism of the grinding unit can be alternatively made in a first form to turn the grinding bit in X-axis, a second form to turn the grinding bit in Y-axis, or a third form to reciprocate the grinding bit.