For example, it is assumed that an actually measured contact pattern as shown in FIG. 17 is obtained as the user operates the pressure sensors 101 a 1, 101 a 2 on the chin portion and the head portion in trying to be identified. [0173] If the data of the actually measured contact pattern is expressed by Di???[ti???,p] (i is an integer), where t??? represents a dimensionless quantity of time, the a