1. A specific call detecting device comprising: an utterance period detecting unit which detects at least a first utterance period in a call between a first speaker and a second speaker, from among the first utterance period in which the first speaker speaks from a first voice uttered by the first speaker and obtained by a voice input unit, and a second utterance period in which the second speaker speaks from a second voice uttered by the second speaker; an utterance ratio calculating unit which calculates utterance ratio of the first speaker in the call on the basis of at least the first utterance period among the first and second utterance periods; a voice recognition execution determining unit which determines whether at least one of the first and second voices is to be a target of voice recognition or not on the basis of the utterance ratio; a voice recognizing unit which detects a keyword related to a specific call from the voice determined as a target of voice recognition among the first and second voices; and a determining unit which calculates an evaluation value so that the larger the number of keywords detected is, the higher the evaluation value indicative of probability of the specific call is, and when the evaluation value is equal to or higher than a predetermined threshold, determines that the call is the specific call.
11. The specific call detecting device according to claim 1 , wherein the lower the utterance ratio is, the more the determining unit increases the evaluation value.