An HPF eliminates an image of an object which is not to be detected from a captured image, thereby obtaining an HPF image. A binarizing unit performs a binarizing process on the HPF image, thereby generating a binary image. A peak detector extracts, using the binary image as a mask, an image of a region corresponding to an opening of the mask from the captured image. From the image, a peak value and the position of a peak pixel are detected. A determining unit determines whether an object to be detected is in contact with the display surface or not on the basis of the relation between the difference and the threshold. Using the detection result and the determination result in the determining unit, a position deriving unit derives the position on the display surface, of the object to be detected which is in contact with the display surface.