A collating device includes a collation list, a collation unit and a comparison unit. The collation list is configured to retain a false alarm list including a registered image, a threshold value serving as a criterion for determining whether to perform alarm activation, and a false alarm person image. The collation unit is configured to collate an input image with the registered image and the false alarm person image managed by the collation list, thereby obtaining a similarity therebetween. The comparison unit is 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 perform the alarm activation.