For an orbital machining in which a spindle having a cutting tool attached thereto and a work to be machined are moved, by feed shaft control, to make a relative displacement to each other along a plane perpendicular to an axis of rotation of the spindle, such that a mutual interpolation motion is achieved between the spindle and the work, and a rotation angle of the spindle is controlled quantitatively and synchronously to have a predetermined correlation to the shaft control so that, at any angular position in rotation of the spindle, a blade direction of the cutting tool is maintained in a preset direction to thereby achieve a cutting into a configuration to be defined by an interpolation locus based on the mutual interpolation motion, there is effected a combination of feed-forward compensation for a follow-up delay in control of a motor servo system of a respective feed shaft and for a follow-up delay in control of a motor servo system of the spindle.