To machine brittle material easily even if objective shape is complicated by vibrating a hammer ultrasonically, and bringing the hammer into contact with the brittle material so that the amplitude direction of the hammer has a normal line component at a contact point with the brittle material.

When a hammer 11 formed of diamond or the like is pressed with suitable force to the surface of brittle material such as glass 1, the vicinity of a part pressed by the hammer 11 is plastically deformed. The surface of a workpiece 1 is therefore hammered continuously by the hammer 11 with suitable roundness at the tip, and this workpiece 1 is relatively moved synchronously with the motion of the hammer 11 to generate a shape by deformation processing. In the case of increasing the machining quantity, the output adjusting volume of an oscillator is operated to adjust for the output increase of alternating voltage applied to a vibrator so as to enlarge the amplitude of the hammer 11.