1. A signal processing apparatus comprising: a segmentalizing unit configured to segmentalize a signal feature quantity which indicates the feature of a content signal into segments having a given time length; a clustering unit configured to cluster the segments corresponding to the signal feature quantity having high level of similarity into a class on the basis of the similarity among the signal feature quantities corresponding to the respective segments; a function deriving unit configured to obtain existence probability functions indicating probabilities that the respective segments exist with respect to an elapsed time period of the content signal for the segments belonging to the respective classes; a similarity calculating unit configured to calculate similarities among the existence probability functions in the respective classes; an integrating unit configured to obtain integrated classes by integrating classes having the existence probability functions with the high level of similarity; and an output unit configured to output identification information on the integrated classes which the respective segments belong to.