A navigation system constructed from a portable terminal device having a route search server provided with route search means for searching for a guidance route from a start point up to a destination; GPS receiving means for positioning a current position; imaging means; and display means for displaying, along with a peripheral image captured by the imaging means, a guidance route, a guidance image in the direction of advance, or an image representing a place of interest. The portable terminal device further has display control means for controlling display of the peripheral image displayed on the display means. The display control means controls the position of display of the peripheral image, captured by the imaging means, so that the center of optical axis of the imaging means is below the center of the display screen. Even if the direction of the optical axis of the imaging means is directed downward from a horizontal line, the horizontal direction of the peripheral image is displayed on the display screen.