To clearly discriminate an object whose state changes in accordance with a background image and to improve detection accuracy of a position indicated by a user.

A first take-in image input from a camera is compared with a second take-in image input after the first take-in image by the prescribed number of frames. A differential area detecting portion 12 detects a difference between the first and second take-in images in the prescribed number of frames in an object whose state changes inside an imaging range. When a part of the detected differential area of the object is overlapped with a detection area which is previously installed in the imaging range, supply information associated with the overlapped detection area is read from a supply information database 14, and the background image overlapped with the supply information is output to an image output portion 17. A position and a shape of the supply information overlapped with the background image are informed to the differential area detecting portion 12, and a supply information invalidating portion 15 invalidates the supply information so that the differential area detecting portion 12 does not detect the difference of the supply information.