1. An image monitoring apparatus, comprising: an overhead camera image analysis unit that receives an image sent from at least one overhead camera that shoots a monitoring area, and detects position information of a monitoring target; a gazing camera image analysis unit that receives images sent from a plurality of gazing cameras that gaze at and shoot areas narrower than the area shot by the at least one overhead camera in the monitoring area, and detects event information that represents the features of the monitoring target; an information integration analysis unit that obtains tracking information about the monitoring target with the use of the position information detected by the overhead camera image analysis unit and the event information detected by the gazing camera image analysis unit; and a gazing camera control signal generation unit that generates control signals for switching gazing targets for the gazing cameras with the use of the position information detected by the overhead camera image analysis unit, the event information detected by the gazing camera image analysis unit, and the tracking information about the monitoring target, and sends the control signals to the gazing cameras respectively; wherein the gazing camera control signal generation unit includes a gazing target selection unit that selects a gazing target for each gazing camera by performing evaluation whether a gazing target candidate for each gazing camera is suitable for a gazing target for each gazing camera or not, wherein the gazing target selection unit performs the evaluation on the basis of the position information detected by the overhead camera image analysis unit, the event information detected by the gazing camera image analysis unit, and the tracking information about the monitoring target, and selects gazing targets suitable for all the gazing cameras respectively by comparing evaluation results for the gazing targets for all the gazing cameras respectively.