An index detecting section detects an index in a physical space, from a captured image obtained by an imaging apparatus. An erroneous-detection prevention processing section performs erroneous-detection prevention processing, based on information relating to image coordinates of a detected index. An image output section outputs, to a display device, an image having been subjected to the erroneous-detection prevention processing. This prevents an image displayed on the display device from being mistaken for a real index when the display device is in the field of view of the imaging apparatus.