1. An area information estimating device comprising: a camera that photographs an image within a sensing area; a person detector that detects a person from the image from the camera; and a position calculator that calculates an existence position of the person in the sensing area based on a coordinate on the image in which the person is detected by the person detector, wherein the person detector excludes the person in whom a relationship between the coordinate and a size on the image does not satisfy a predetermined condition from a detection target.