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.