Head-up display and program product

A head-up display comprising:

• a display unit displaying images in a display region defined on a windshield of a vehicle;
• a vehicle information acquisition unit acquiring a vehicle information indicative of an operation state of the vehicle;
• a forward view information acquisition unit acquiring a forward view information indicative of a forward view of the vehicle in a traveling direction;
• a display object detection unit detecting, based on the forward view information and the vehicle information, a display object for which a guidance information is required to be displayed in the display region defined on the windshield;
• a display control unit generating a guidance image to be displayed on the windshield so that the guidance image indicates the guidance information of the display object detected by the display object detection unit and is superimposed over the display object when seen from an inside portion of a compartment of the vehicle, and the display control unit displaying the generated guidance image on the windshield using the display unit so that the guidance image is superimposed over the display object;
• and
• a display form setting unit calculating, based on the vehicle information, or based on both the vehicle information and the forward view information, a changing rate of the forward view and a changing rate of the guidance image when the guidance image is displayed on the windshield in a superimposed manner, wherein each of the changing rate of the forward view and the changing rate of the guidance image is calculated based on a vehicle speed and increases with an increase of the vehicle speed, and the display form setting unit setting a display form of the guidance image generated by the display control unit under a condition that a sum of the changing rate of the forward view and the changing rate of the guidance image is within a predetermined appropriate range.