We propose an instant posture estimation technique, which can operate only by a stereo image with small (6 cm) baseline. It does not require a priori information of the target user, background information, and markers. This system allows cameras to move freely, because it operates only with a small stereo camera unit. Moreover, if the input image is replaced with a movie or real-time video, this system can be used as a real-time motion tracker. With our proposed technique, robots and computers will be able to non-verbally communicate with unspecified people as well as pre-registered people. Moreover, this system can output not only the posture but also the body size and clothes. Therefore, proposed technique can also be used as a calibration procedure for other motion tracking algorithms.