The present invention is to eliminate formation of a shape that induces reduction of fatigue strength, without forming a step part, in a shape portion formed by machining. This processing apparatus includes end mills having bottom blades formed in a curved convex shape, and arcuately formed radial blades provided in corner areas; a drive section for driving the end mills; and a control unit for controlling the drive unit. The control unit includes a planar-shape-formation unit that controls the drive unit so as to form, in a workpiece, only a planar-shape portion adjacent to a fillet shape portion in such a manner that a portion of the shape to be processed corresponding to the fillet shape portion is left unprocessed; and a fillet formation unit that controls the drive unit so as to form the fillet shape portion in the workpiece in a single pass using the radial blades.