1.  Technical Field
The present invention relates to a technology of creating or updating registration information (dictionary) containing a characteristic parameter of a given voice and to a technology of checking a characteristic parameter of a voice input by a user (hereinafter called “input voice”) against a characteristic parameter of a given voice contained in the registration information. 
2.  Related Art
Conventionally, technologies of certifying the correctness of a speaker (speaker authentication) and of specifying a speaker among a plurality of registrants (speaker identification) have been proposed.  In the speaker authentication and the speaker identification, voice registration and checking are carried out.  At the stage of the registration, registration information is created based on a characteristic parameter extracted from an input voice, and at the stage of checking, a characteristic parameter of another input voice is checked against a characteristic parameter of the registration information (for instance, Non-Patent document 1 and Non-Patent document 2).     [Non Patent document 1] Tomoko MATSUI, “Speaker Recognition using HMM”, Technical report of IEICE, The Institute of Electronics, Information and Communication Engineers (IEICE), January 1996, SP 95-111, pp.  17 to 24    [Non Patent document 2] Shoji HAYAKAWA and two others, “Speaker recognition using individual information in harmonic structure of linear predictive residual spectrum” Journal of IEICE, The Institute of Electronics, Information and Communication Engineers (IEICE), September 1997, A Vol.  J80-1 No.  9, pp 1360 to 1367
However, a voice input at the time of the registration may not be suitable for creating and updating the registration information in some cases.  For instance, in the case where the quantity of the input voice is extremely small, it is difficult to extract a characteristic parameter appropriately, and as a result the actually created registration information may be disconnected from the original feature of the speaker.  Thus, there is a problem of degradation in the accuracy of the checking using the registration information.  Similarly, if the input voice for the voice checking is inappropriate, even when the registration information sufficiently reflects the original feature of the speaker, the accuracy of the checking will be degraded.