To increase the number of object for which position, posture, and so forth are regularly updated even when a viewpoint position and a viewing direction are constantly changed in a virtual three-dimensional space, while keeping deterioration in smoothness of a display image unnoticeable. An image processor for producing and displaying a display image showing a picture obtained by viewing a virtual three-dimensional space where a viewpoint and a plurality of display target objects are disposed, from the view point, comprises an object selection unit (66) for calculating a display size, in the display image, of each of the plurality of display target objects and selecting some of the plurality of display target objects based on the calculated display size of each of the plurality of display target objects, and a state update unit (68) for updating a state of the objects selected by the object selection unit (66) in the virtual three-dimensional space at a time interval different from that for other objects in the virtual three-dimensional space.