Grinding machining device and control method for the same

Provided is a technique making it possible to grind a workpiece with high-precision even if there is a need for a processing force such as would produce elastic deformation in a mechanism. A feeding means supports a grindstone and/or a workpiece so that the same can move in a feeding direction, and during grinding processing, draws the workpiece and the grindstone closer to each other, into contact with each other, and apart from each other. A processing force detecting means detects a processing force, which is the force of the grindstone being pushed against the workpiece by the feeding means. A position detecting means detects a grindstone position, which is a position of the grindstone in the feeding direction in relation to a mounting position of the workpiece. A controlling means composites, at a predetermined ratio, a control amount in positioning control that controls the grindstone position detected by the position detecting means so as to be a desired position, and a control amount in processing for