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 of a person who is not to be alarmed and who was previously erroneously alarmed due to having been mistaken for another person who is to be alarmed; a collator configured to collate an input image with the registered image and the false alarm person image managed by the collation list, such that the collator obtains a similarity between the input image with the one of the registered image and the false alarm person image; and a comparator configured to compare: a larger one of a value of the obtained similarity between the input image and the false alarm person image, and the threshold value; and the similarity between the input image and the obtained registered image, such that the comparator determines whether to perform the alarm activation.