A grinding wheel dresser with a diamond-tipped dressing tool carried by a pivotally mounted arm driven by a fluid-actuated drive to sweep the diamond tip across the working surface of a grinding wheel. The arm and fluid-actuated drive are carried by an arbor mounted for rotation in a housing and having a knob secured thereto so that the arbor can be manually rotated to angularly orient the path of the diamond tip with respect to the working face of the grinding wheel to permit the dressing of work surfaces with differing contours and inclinations to the axis of rotation of the wheel.