1. A signal detection system that searches for a part of a stored signal similar to a target signal, comprising: a stored feature calculation portion that calculates a stored feature from the stored signal; a target feature calculation portion that calculates a target feature from the target signal; and a feature comparison portion that calculates a degree of similarity using both a vector generated by degenerating the stored feature based on statistics of the stored feature calculated beforehand and a vector generated by degenerating the target feature based on statistics of the target feature calculated beforehand, wherein the signal detection system is a sound signal detection system that searches for a part of a stored sound signal that is the stored signal similar to a target sound signal that is the target signal having a shorter or same length as the stored sound signal, the stored feature calculation portion that calculates the stored feature from time-series data of the stored sound signal, the target feature calculation portion that calculates the target feature from time-series data of the target sound signal, the sound signal detection system further comprises: a stored feature area selection portion that calculates predetermined statistics from the stored feature, selects an element from the stored features corresponding to the statistics larger than a predetermined threshold, and calculates a stored area selection feature generated from a vector of the selected element; and a target feature area selection portion that calculates predetermined statistics from the target feature, selects an element from the target features corresponding to the statistics larger than a predetermined threshold, and calculates a target area selection feature generated from a vector of the selected element, and the feature comparison portion sets a comparison segment in the stored area selection feature, calculates a degree of similarity between the target area selection feature and the comparison segment of the stored area selection feature, repeats calculating while shifting the comparison segment one by one in the stored area selection feature, and searches for an area of the stored area selection feature similar to the target area selection feature.