1. A signal detection system which detects signals similar to a target signal from stored signals which are stored, comprising: a target signal feature quantity calculation section which derives a feature quantity series from a target signal; a stored signal feature quantity calculation section which derives a feature quantity series from a stored signal; a target signal histogram calculation section which sets a predetermined observation window in a feature quantity series derived in said target signal feature quantity calculation section, and calculates a histogram of the feature quantities within said observation window; a stored signal histogram series calculation section which obtains a histogram series in regard to a feature quantity series derived in said stored signal feature quantity calculation section, by sequentially setting a predetermined observation window with respect to each section of a size which corresponds to said observation window, and calculating a histogram of feature quantities within said observation window; a stored signal histogram grouping section which groups histogram series sets in a histogram series obtained from said stored signal histogram series calculation section, for which a mutual similarity level calculated with a predetermined L1 distance measure satisfies a predetermined criteria; a stored signal histogram group selection section which determines the existence of a possibility of the inclusion of an area which should be output from within a histogram group obtained in said stored signal histogram grouping section, and selects the group which has a possibility; a stored signal collation section which performs collation with respect to histograms belonging to a histogram group selected in said stored signal histogram group selection section, by said predetermined L1 distance measure, and obtains a similarity value; and a collation result output section which determines whether or not the collated area is to be made a detection result, by the similarity value obtained in said stored signal collation section, and outputs the collated area in a case where it has been determined it is to be made a detection result.