PURPOSE: To make it possible to automate grinding operation by grinding a workpiece under pushing a grinding unit against the workpiece by means of a balance cylinder with the grinding unit opposed to the curved face of the workpiece in a curved face grinding device for cast iron or the like.

CONSTITUTION: The side section of a workpiece supporting device 2 is provided with a movable body 24 freely adjustable of a position back and forth, right and left, and up and down. A supporting base 26 equipped with a grinding unit 43 is provided in front of the movable body 24 through a horizontal shaft 27 so as to be capable of freely swinging vertically. And between the movable body 24 and supporting base 26 is provided a balance cylinder 28 for swing of which the pushing work chamber is pneumatically operated and the pulling work chamber hydraulically. In grinding a curved face 6a with a grind-stone 51, the movable body 24 is transfered by a transfer cylinder 25, and the supporting base 26 is made to swing by the cylinder 28 to make the grinding unit 43 trace the curved face 6a performing grinding finish. Then, the unit 43 is shifted one pitch by one pitch with a motor 19 performing grinding finish to the whole curved face.