A system and method extract off-topic parts from a conversation. The system includes a first corpus including documents of a plurality of fields; a second corpus including only documents of a field to which the conversation belongs; a determination means for determination as a lower limit subject word a word for which IDF value for the first corpus and IDF value for the second corpus are each below a first certain threshold value; a score calculation part for calculation as a score a TF-IDF value for each word included in the second corpus; a clipping part, for sequential cutting out of intervals from text data that are contents of the conversation; and an extraction part for extraction as an off-topic part an interval where average value of the score of words included in the clipped interval is larger than a second certain threshold value.