1. A voice data analyzing device comprising: a speaker model deriving unit which derives speaker models as models each specifying character of voice of each speaker from voice data including a plurality of utterances to each of which a speaker label as information for identifying a speaker has been assigned; and a speaker co-occurrence model deriving unit which derives a speaker co-occurrence model as a model representing the strength of a co-occurrence relationship in which a plurality of speakers appear in a same conversation, among the speakers from session data obtained by segmenting the voice data in units of sequences of conversation by use of the speaker models derived by the speaker model deriving unit.
2. The voice data analyzing device according to claim 1 , further comprising a speaker estimation unit which estimates the speaker label for an utterance which has been assigned no speaker label by at least referring to the speaker models or the speaker co-occurrence model already derived at that point in cases where the voice data inputted to the speaker model deriving unit or the speaker co-occurrence model deriving unit includes such an utterance to which no speaker label has been assigned.