To provide a technology which allows workpiece to be ground with high accuracy even when a machining force to cause elastic deformation in a mechanism is required.

A feeder movably supports a grindstone and/or a workpiece in a feeding direction and, during grinding machining, the workpiece and grindstone are approached, brought into contact, or separated. Machining force detection means detects a machining force to be a force by which the grindstone is abutted by the feeder to the workpiece. Position detection means detects a grindstone position to be a position in the feeding direction of the grindstone with respect to an attachment position of the workpiece. Control means synthesizes a control amount of positioning control which controls the grindstone position detected by the position detection means at a desired position with a control amount of machining force control for controlling the machining force detected by the machining force detection means to a desired machining force at a prescribed rate and executes control.