1. A feature-vector generation apparatus comprising: an input unit configured to input content data including at least one of video data and audio data; a variable-part detection unit configured to detect, in the content data, a variable part which (A) if the content data is broadcast, is subject to replacement or omission depending on (i) broadcasting dates and hours of the content data, (ii) broadcasting stations, and/or (iii) broadcasted area, or (B) if the content data has been recorded in a recording medium, is different from the version recorded in the recording medium; a generation unit configured to generate a feature vector, identifying periods ranging from start of modified content data acquired by excluding the variable part from the content data to each of plural times at which at least one of a scene change, a silent zone, and a state in which a sound level is not less than a preset level of the modified content data appears; and a storage unit configured to store the content data and the feature vector.