Landslide of the Whanpyeong Mountain which was occurred at Busan Metropolitan City in 1999 belongs to the category of plane failure. Automatic monitoring system to measure horizontal displacement, pore pressure change and load change has operating from reconstruction stage for evaluating rock slope stability (August, 2000$~$Feburuary, 2002). As a result of the analysis on the monitoring performance data, it is suggested that infiltrated rain water from pound surface discharges rapidly through cut-slope because pressure head of water decreases rapidly after rainfall while rise of pore pressure is proportional to the amount of rain water. As a result of data analyses for inclinometers and load cells, it seems that slope is stablized be cause ground deformation is rarely detected. The areas especially similar to the study site where landslide is induced by heavy rain fall, change of pore pressure is rapidly analyzed using automatic monitoring system. Therefore, it is considered that automatic monitoring system is very effect for slope stability analysis on important cut-slopes.