A folding-type mobile terminal device having a navigation function, the mobile terminal device forming either one of an open style and a closed style by two or more movable casing units (100A, 100B), said mobile terminal device comprising: a direction detection unit (180, 110) adapted for detecting a direction of the mobile terminal device; a position detection unit (170, 110) adapted for detecting a current position of the mobile terminal device; a style detection unit (160, 110) adapted for detecting whether the mobile terminal device is in the open style or in the closed style based on the conditions of the casing units (100A, 100B); a first display unit disposed to be viewable when the mobile terminal device is in the open style; and a second display unit disposed to be viewable when the mobile terminal device is in the closed style, characterized by a display control unit adapted for controlling the first display unit so as to display a detailed navigation screen showing a route from a current position to a designated destination when the style detection unit (160, 110) detects that the mobile terminal device is in the open style, and for controlling the second display unit so as to display a simple navigation screen showing a direction toward the destination with respect to the current position when the style detection unit (160, 110) detects that the mobile terminal device is in the closed style; and a direction calculation unit adapted for calculating the direction to the destination with respect to the current position detected by the position detection unit (170, 110) in accordance with the direction detected by the direction detection unit (180, 110), when the simple navigation screen is displayed by the display control unit, wherein the display control unit generates the simple navigation screen showing the direction calculated by the direction calculation unit, and displays the generated simple navigation screen in accordance with a forward direction based on the direction of the mobile terminal device detected by the direction detection unit. a direction detection unit (180, 110) adapted for detecting a direction of the mobile terminal device; a position detection unit (170, 110) adapted for detecting a current position of the mobile terminal device; a style detection unit (160, 110) adapted for detecting whether the mobile terminal device is in the open style or in the closed style based on the conditions of the casing units (100A, 100B); a first display unit disposed to be viewable when the mobile terminal device is in the open style; and a second display unit disposed to be viewable when the mobile terminal device is in the closed style, characterized by a display control unit adapted for controlling the first display unit so as to display a detailed navigation screen showing a route from a current position to a designated destination when the style detection unit (160, 110) detects that the mobile terminal device is in the open style, and for controlling the second display unit so as to display a simple navigation screen showing a direction toward the destination with respect to the current position when the style detection unit (160, 110) detects that the mobile terminal device is in the closed style; and a direction calculation unit adapted for calculating the direction to the destination with respect to the current position detected by the position detection unit (170, 110) in accordance with the direction detected by the direction detection unit (180, 110), when the simple navigation screen is displayed by the display control unit, wherein the display control unit generates the simple navigation screen showing the direction calculated by the direction calculation unit, and displays the generated simple navigation screen in accordance with a forward direction based on the direction of the mobile terminal device detected by the direction detection unit.