1. A behavior estimating system for estimating a behavior manner of an instructor, comprising: a state recognizing element which recognizes a position of a state variable, which is displaced as the instructor moves, at one or a plurality of reference time points as the position of one or a plurality of reference points; and a trajectory generating element which generates, on the basis of the position or positions of the reference point or points recognized by the state recognizing element, a plurality of estimated trajectories representing estimated positions of the state variable in a time-series manner according to a plurality of first models which correspond to a plurality of behavior manners of the instructor and represent shape characteristics of individual reference trajectories indicative of the time-series changing manners of the position of the state variable and a second model which represents a motion of the instructor in which the position of the state variable and one or a plurality of n-th order time differential values (n=1, 2,. .. ) thereof continuously change, under a condition that the estimated trajectories pass the reference point or points or a range or ranges in the vicinity thereof, wherein fluctuations of the first models are allowed, stabilities of the first models in the process of generation of the plurality of estimated trajectories by the trajectory generating element are assessed on the basis of cumulative amounts of the fluctuations, and a behavior manner corresponding to one of the first models which exhibits a highest stability is estimated as a behavior manner of the instructor.