This study was performed to investigate machining phenomena by observing and analyzing the changes in dynamic workpiece internal stress distribution in the ultrasonic band caused by ultrasonic vibration cutting in the thrust direction utilizing the photoelastic method and photography by synchronizing the light source and orthogonal cutting model. The tool relief angles used in the experiments were 10°, 20,° and 30°. The compressive stress distribution was observed in front of the cutting edge, and the stress action area reached the maximum at the lowest relative position between the tool and the workpiece. Moreover, the stress action area increased in with decreasing tool relief angle. This was because smaller tool relief angle resulted in a larger interference area in one period of ultrasonic vibration.