In order to secure inhabitants from a landslide, a remote and wide coverage monitoring with a high time-series resolution is demanded to detect any further events on the landslide slope. GB-SAR is a technique that possesses these features and suitable for the purpose. We installed a GB-SAR system at a post-landslide site to monitor. A preliminary experiment at the site showed that the system is capable to measure a few millimeter movements of a corner reflector placed at a distance of 450 m with an accuracy of a few tenths of millimeters, which should be accurate enough to detect displacement on the landslide slope. Furthermore, at the time of an earthquake, the GB-SAR system successfully detected a very localized displacement on the slope, which may indicate a small-scale landslide.