A rotation axis of a work spindle and a rotation axis of a spindle primary-axis portion are rotated relative to each other and feeding of a work-piece to a tool is accordingly adjusted, whereby warpage of the tool in accordance with a change in machining condition is corrected. A revolution volume of the relative rotation is compared and calculated in process based on data entered in advance, a result of measurement by a displacement sensor and information such as a machining position, and controlled in real time until the end of machining. The relative rotation is driven by an actuator such as a piezoelectric element, at a resolution even as fine as in seconds. The data entered in advance can be sequentially updated in accordance with monitoring of a processed product.