1. A collating device comprising: a collation list configured to retain a false alarm list comprising a registered image, a threshold value serving as a criterion for determining whether to perform alarm activation, and a false alarm person image; a collation unit configured to collate an input image with the registered image or the false alarm person image managed by the collation list, thereby obtaining a similarity therebetween; and a comparison unit configured to compare: a larger one of a value of the similarity between the input image and the false alarm person image, which is obtained by the collation unit, and the threshold value; and the similarity between the input image and the registered image, which is obtained by the collation unit, thereby determining whether to perforin the alarm activation.