Giving a natural operational feeling to a human via a haptic interface requires not only a sophisticated and intuitive mechanical design, but also an appropriate control system design. Most haptic systems, however, implicitly demand that the human gets used to manipulation of the haptic devices before he/she can get the feel of the virtual space and/or telepresence beyond the haptic device. Based on a new concept of a human-in-the-loop system called Human Adaptive Mechatronics (HAM), an assist-control for a force/vision interactive haptic system is discussed in this paper. The proposed assist-control scheme includes online estimation of a operator's control characteristics, and a 'force assist' function implemented as a change in the support ratio according to the identified skill level. We developed a HAM haptic device test system, performed evaluation experiments with this apparatus and analyzed the measured data. It was confirmed that the operator's skill could be estimated sufficiently and that operator's performance was enhanced by the assist-control.