In this study, the movement of tungsten wire electrode during fine wire EDM was investigated by the direct observation using high-speed video camera. The results showed that the vibration amplitude and frequency depended mainly on the wire tension, and the amplitude direction. The amplitude in the direction parallel to the machining direction was a little larger than that in the perpendicular one. Also, the backward deflection of wire could be confirmed even in fine wire EDM. Furthermore, the wire vibration mode was analyzed, and it could be varied with the machining position of the thin workpiece, which possibly led to smaller wire amplitude.