PURPOSE: To obtain the action of smooth dressing in good efficiency enabling the parallelness with a table surface to be held with no play, by driving a grinding wheel dresser driving gear through a hydraulic cylinder.

CONSTITUTION: A cylinder 2 is actuated automatically advancing and retracting in a certain fixed speed by the action of inlet and outlet parts of a hydraulic circuit unit 1. And the cylinder 2 provides in its point end a connecting shaft 8, which fixedly connects a dresser upper and bottom part cut-in setting device 5, to be fixed by a guide 4 with no clearance. Consequently, dressing of a grinding wheel 6 can be performed by the preset depth of cut parallelly with a grinding wheel shaft 7 in accordance with the guide 4 while vibration of a shaft of the cylinder 2 is suppressed. Accordingly, the action of smooth dressing can be obtained being able to hold the parallelness with a table surface by automatically and efficiently actuating a dresser 3 further with no generation of a play.