A unit (110) acquires an image, sensed by an image sensing device (100), of a physical object having an outer appearance that can be expressed by line segments. A unit (120) stores defining data used to classify line segments configuring a 3D virtual object that simulates the outer appearance of the physical object into a plurality of groups and to define respective line segments belonging to the groups. A unit (130) selects one group from the groups one by one without any repetition. The unit (130) projects line segments which belong to the selected group onto a physical space using the defining data used to define that line segments, and the image of the physical space. The unit (130) then updates a position and orientation of the image sensing unit based on the line segments projected onto the physical space and a feature in the image of the physical object.