3. The interesting section identifying device of claim 2 , further comprising a reference index calculating unit configured to calculate a reference vector based on a plurality of second unit section frequency vectors in a reference section composed of a plurality of continuous second unit sections that include the designated time, and to assign, to the reference value, a largest one of the variances of the second unit sections included in the reference section, wherein the interesting section candidate extracting unit initially designates the reference section as a temporary interesting section candidate and repeats a process of (i) determining whether the second unit section frequency vector of a second unit section adjacent to the temporary interesting section candidate has at least a predetermined correlation to the reference vector and (ii) including the second unit section adjacent to the temporary interesting section candidate in the temporary interesting section candidate when determining that the second unit section frequency vector and the reference vector have at least the predetermined correlation, the interesting section candidate extracting unit terminating repetition of the process and designating the temporary interesting section candidate as the interesting section candidate upon determining that the second unit section frequency vector and the reference vector do not have at least the predetermined correlation.
3. The interesting section identifying device of claim 2 , further comprising a reference index calculating unit configured to calculate a reference vector based on a plurality of second unit section frequency vectors in a reference section composed of a plurality of continuous second unit sections that include the designated time, and to assign, to the reference value, a largest one of the variances of the second unit sections included in the reference section, wherein the interesting section candidate extracting unit initially designates the reference section as a temporary interesting section candidate and repeats a process of (i) determining whether the second unit section frequency vector of a second unit section adjacent to the temporary interesting section candidate has at least a predetermined correlation to the reference vector and (ii) including the second unit section adjacent to the temporary interesting section candidate in the temporary interesting section candidate when determining that the second unit section frequency vector and the reference vector have at least the predetermined correlation, the interesting section candidate extracting unit terminating repetition of the process and designating the temporary interesting section candidate as the interesting section candidate upon determining that the second unit section frequency vector and the reference vector do not have at least the predetermined correlation. 11. The interesting section identifying device of claim 3 , wherein the detailed structure determining unit determines whether the detailed structure is included in every second unit section throughout the interesting section candidate.