1. A monitoring system comprising: an intrusion detecting section for detecting an intruding object in a monitoring area, to generate a stop signal for stopping an operation of an external device; a camera for photographing the monitoring area; a detail check image generating section for generating a detail check image for display based on a camera image photographed by the camera; a privacy image generating section for generating a privacy image with lower picture quality than picture quality of the detail check image based on the camera image; a display image selecting section for selecting either the detail check image or the privacy image as a display image; and an image displaying section for displaying the display image selected by the display image selecting section.