1. A monitoring system comprising: an intrusion detecting section configured to detect an intruding object in a monitoring area, to generate a stop signal for stopping an operation of an external device; a camera configured to photograph the monitoring area; a detail check image generating section configured to generate a detail check image for display based on a camera image photographed by the camera; a privacy image generating section configured to generate 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 configured to select either the detail check image or the privacy image as a display image; an image displaying section configured to display the display image selected by the display image selecting section, a light projector configured to generate detection light; a light receiver configured to receive the detection light reflected by a target, to generate a detection signal; a scanning section configured to perform a scan with the detection light in a circumferential direction about a rotational axis, along a scanning surface intersecting with the rotational axis; and a distance measuring section configured to obtain a distance to the target based on the detection signal, wherein the intrusion detecting section detects an intruding object in the monitoring area based on the distance to the target and a scanning angle of the detection light, the camera is arranged above the scanning surface in terms of the rotational axial direction, and the privacy image generating section specifies a boundary line made up of a position of the target on the scanning surface based on the distance to the target and the scanning angle of the detection light, and takes a band-like region including the boundary line in the privacy image as a focused monitoring region, to match picture quality of the focused monitoring region with picture quality of the detail check image.