A motion detecting system which can set a proper set value for motion detection processing carried out by a camera server through a setting terminal. A setting terminal is connected to a camera server via a network for communication with each other. In the camera server, first motion detection processing is carried out for detecting a variation in an image taken by a camera based on a first set value. In the setting terminal, second motion detection processing is carried out on the taken image acquired based on a second set value via the network. The second set value is transmitted to the camera server so as to change the first set value according to a result of the second motion detection processing.