A detection area is decided in a case where a target has gone out-of-frame. If a target is being imaged by a camera continuously, it is determined whether the target has gone out-of-frame. If the target has gone out-of-frame, then the magnitude and direction of motion of the camera are detected. If camera motion is large, it can be concluded that the camera user is imaging the target while tracking it. Accordingly, it can be concluded that the target will again be imaged at the center of the imaging zone. An area defined as a region in which the target will be detected is set at the center of the imaging zone. If camera motion is small in a case where the target goes out-of-frame, it can be concluded that the user is waiting for the target to re-enter the imaging zone and therefore the edge of the imaging zone is set as the detection area.