PURPOSE: To provide a grinder suitable for processing a piece of work excellently in flatness and accurately at an item.

CONSTITUTION: A dressing grinding wheel 9 is arranged at a position linearly symmetrical with work W to the axis core of a cup type grinding wheel 2, and also is provided so that the end surface of the dressing grinding wheel 9 can abut on part of the tip surface of the cup type grinding wheel 2. In grinding work with the cup type grinding wheel 2, not only part of the end surface of the work W but concurrently also part of the end surface of the dressing grinding wheel 9 abut on the tip surface of the cup type grinding wheel 2, and also when the cup type grinding wheel 2 is tilted more at the time of grinding than before the grinding by comparing, the abutting ford of the dressing grinding wheel 9 is adjusted with a pushedly pressing rod 13 to correct the tilt of the cup type grinding wheel 2 to a condition before grinding for surely preventing the tilt of the grinding wheel axis of the cup grinding wheel 2.