Rainfall and melting snow infiltrate fissures and aquifers, often triggering landslides on slip surfaces. This pa per presents five typical landslide areas for which the depth of slip surface was determined and time series data of groundwater level and slide displacements. The relation between the displacement of the slide and the pore water pressure was examined especially closely. The useful results obtained are summarized below. (1) The relations between the displacement of slide and the

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... water pressure are classified into three types. The first is a type of rock mass landslide that is sensitive to the pore water pressure the whole year round. In the relation curve of the velocity of displacement versus the pore water pressure, there is practically no hys teresis for the pressure increasing period and the pressure decreasing period. The second is a type of rock mass landslide that moves mainly in the snow melting period. The curve of the velocity of displacement ver sus the pore water pressure indicates hysteresis for the pressure increasing period and the pressure decreas ing period. The third type is the detritus landslide consisting of pelitic-schist. In this type, the displacement peak occurs after the pressure peak.