1. An electronic endoscope system comprising: an electronic endoscope that can be inserted into a test subject to capture images of the interior of the test subject; a changed-area detecting device for detecting a changed area in an image captured by said electronic endoscope using data of the captured image, the changed area having different features from other area of the captured image; a mask data producing device for producing mask data based on the detected changed area, the mask data allocating an image processing parameter to each pixel of the captured image such that the changed area is processed in a different way from the other area; and an image processing device for processing the captured image according to the mask data.