Provided is a suspicious person detection method. First, a normal similar facial image search is carried out. Next, facial images, which are detected automatically from the input images and specified manually, are specified to be determined. Next, similar faces are searched for limited time on a time axis on the database. Next, the number of search results that distance between the features is lower than predetermined value is calculated and it is determined that the number of appearances is large and a possibility of a prowling person is high if the number of cases is large, and otherwise a possibility of prowling person is low. Last, a similarity between a facial image of a pre-registered residents and a facial image of a person whose number is large is calculated, and it is re-determined that the person is residents if the similarity is high, regardless of the determination.
