An area information estimating device comprising: a camera configured to photograph an image of a sensing area; a person detector configured to detect a person from said image photographed with the camera by acquiring a detection coordinate and the size of a detection rectangle surrounding the detected person as detection result, and configured to output said detection result to a position calculator, wherein the person detector excludes a detection result with respect to a person in whom a relationship between the detection coordinate and the size on the image does not satisfy a predetermined condition; said position calculator configured to calculate an existence position of the person in the sensing area, detected by the person detector, using said detection coordinate on the image in which the person is detected by the person detector and the size of said detection rectangle surrounding the detected person, by performing processing of transforming said detection coordinate (X,Y) into a position coordinate (T,L) on a floor surface in a real space by a geometric calculation in which already-known parameters of the camera are used, the existence position being a position corresponding to said position coordinate (T,L), where the person detected by the person detector is calculated to exist on said floor surface in a real space in the sensing area; and a position storage in which existence positions, calculated by the position calculator, of persons detected by the person detector are stored; wherein the area information estimating device further comprises an estimator configured to estimate an existence allowable area being said floor surface in the real space and where a person can exist in the sensing area using the probability density distributions of stored existence positions of persons detected in a predetermined period in the sensing area; wherein the estimator superposes each detected existence position on plan view in a form of said probability density distributions, and determines an area where a cumulative probability becomes greater than or equal to a predetermined level as the existence allowable area; wherein the estimator is configured to determine said probability density distribution of each detected existence position by providing probability values around the respective detected existence position, the detected existence position having a maximum probability value, as said probability density distribution of the detected existence position, wherein the probability density distribution of said respective detected existence position is longer in a depth direction when viewed from the camera than in a direction orthogonal to the depth direction. a camera configured to photograph an image of a sensing area; a person detector configured to detect a person from said image photographed with the camera by acquiring a detection coordinate and the size of a detection rectangle surrounding the detected person as detection result, and configured to output said detection result to a position calculator, wherein the person detector excludes a detection result with respect to a person in whom a relationship between the detection coordinate and the size on the image does not satisfy a predetermined condition; said position calculator configured to calculate an existence position of the person in the sensing area, detected by the person detector, using said detection coordinate on the image in which the person is detected by the person detector and the size of said detection rectangle surrounding the detected person, by performing processing of transforming said detection coordinate (X,Y) into a position coordinate (T,L) on a floor surface in a real space by a geometric calculation in which already-known parameters of the camera are used, the existence position being a position corresponding to said position coordinate (T,L), where the person detected by the person detector is calculated to exist on said floor surface in a real space in the sensing area; and a position storage in which existence positions, calculated by the position calculator, of persons detected by the person detector are stored; wherein the area information estimating device further comprises an estimator configured to estimate an existence allowable area being said floor surface in the real space and where a person can exist in the sensing area using the probability density distributions of stored existence positions of persons detected in a predetermined period in the sensing area; wherein the estimator superposes each detected existence position on plan view in a form of said probability density distributions, and determines an area where a cumulative probability becomes greater than or equal to a predetermined level as the existence allowable area; wherein the estimator is configured to determine said probability density distribution of each detected existence position by providing probability values around the respective detected existence position, the detected existence position having a maximum probability value, as said probability density distribution of the detected existence position, wherein the probability density distribution of said respective detected existence position is longer in a depth direction when viewed from the camera than in a direction orthogonal to the depth direction.