An image display controlling unit controls to display a standard image and a dummy image. The standard image is an image that has been previously decided by the user. The dummy image looks like the standard image but the standard image and the dummy image has differences that only the user can identify and that can not be identified from a distance. The user selects a predetermined section of the standard image and selects a dummy section from the dummy image. A password is input based on information corresponding to the predetermined section of the standard image and information corresponding to the dummy section of the dummy image is neglected.