An image including the marker M is continuously collected every constant time from the images and template matching is performed by utilizing the first template image stored in advance in the template image memory element relative to the image including the marker M. And the image including the marker M after pattern matching specified by the template matching element is clipped as a template image and is stored in the template image memory. Then, the image including the marker M is acquired from the next images continuously collected every constant time. Thereafter, the template matching is performed by utilizing the second template image stored just therebefore in the template image memory element relative to the image including the marker M. Once the second template matching is completed, the image including the marker M is clipped as the next second template image since the pattern matching is identified by the template matching element, and is stored. For the next template matching, the second template image newly stored is utilized.
