1. A method of monitoring a moving object within a predetermined monitoring area, the method comprising: repeatedly detecting objects every predetermined determination period of time for monitoring objects in the monitoring area by scanning the monitoring area with use of an optical distance meter; identifying the moving objects among the detected objects in each of the determination periods; setting, as a tracking target, among the identified moving objects, a moving object which is present in the monitoring area and which is newest identified, wherein the tracking target is tried to be repeatedly set in each of the determination periods; automatically tracking the moving object which has been set as the tracking target, with use of a camera device every time the tracking target is set, wherein, when there are present a plurality of moving objects which are identified as being the newest, the tracking target is set in an order of starting from a moving object located the nearest to a border of the monitoring area, and the identified tracking target is automatically tracked, the setting and the automatically tracking being repeated for all the identified moving objects; determining whether or not a plurality of the moving objects are identified in the monitoring area; determining whether or not a predetermined tracking release condition, which is set for releasing the automatic tracking using the camera device has been met when it is determined that the plurality of the moving objects are identified in the monitoring area; and enlarging and monitoring, in fixed-point monitoring, preset priority monitoring areas including the priority monitoring object present in the monitoring area with use of the camera device, when it is determined that the tracking release condition is met.