Landslides are gravitational mass movements of rock, debris or earth. Shear deformation in landslides before failure conforms to the field of statics. But shear deformation during seismic loading and post-failure motion of landslides conforms to the field of dynamics. Thus, study of the initiation of earthquake-induced landslides and rapid landslide motion needs to develop “Landslide dynamics” involving dynamic loading and dynamic generation/dissipation of excess pore-water pressure during motion. New developments in science can be facilitated by new technological advances. This study aimed to develop a new testing method that can geotechnically simulate the formation of the shear zone and the following long and rapid shear displacement that occurs in high-velocity landslides. Sassa K and his colleagues at DPRI (Disaster Prevention Research Institute), Kyoto University, have worked to develop an undrained stress-controlled dynamic-loading ring-shear apparatus and its testing method for this purpose. This paper describes the development of this testing method, and its application to the study of earthquake-induced landslides and landslide triggered debris flows in Japan.