1. A head-mounted display device with which a user can visually recognize a virtual image and an outside scene, the head-mounted display device comprising: an image display unit configured to cause the user to visually recognize the virtual image; an outside-scene acquiring unit configured to acquire outside scene information including at least a feature of the outside scene in a visual field direction of the user; a position estimating unit configured to estimate, on the basis of at least two kinds of the outside scene information acquired by the outside-scene acquiring unit over time, a position of any target object present in a real world; and an augmented-reality processing unit configured to cause the image display unit to form, on the basis of the estimated position of the target object, the virtual image representing a virtual object to be added to the target object.