1. A monitoring system comprising: a plurality of cameras each of which monitors a monitor area and has a changeable imaging magnification; monitoring section which detects an object to be monitored in the monitor area; and control section which selects at least one camera capable of obtaining an enlarged image to contribute to identification of the object to be monitored as camera for enlargement from the plural cameras when the object to be monitored is detected and selects at least one camera other than the camera for enlargement as camera for wide area from the plural monitoring camera, said control section setting the camera for wide area to a first imaging magnification to obtain a wide area image of the monitor area, and setting the camera for enlargement to a second imaging magnification larger than the first imaging magnification to obtain an enlarged image of the detected object to be monitored.