In recent years, the observation of single protein molecules has made a phenomenal development, and it has become possible to observe molecular dynamics in vivo at high-speed and with high accuracy. In conventional DXT (Diffracted X-ray Tracking), by labeling with a gold nanocrystal a specific site of a target protein molecule and by observing the positional change of the diffracted X-ray spots from the labeled gold nanocrystal with time-resolution of micro-second and pico-meter precision, we could successfully measure the internal motions of single molecules using DXT.