After a heavy snowfall between Dec 28, 2010 and Jan 4, 2011, a landslide occurred on a cut slope at the rear mountain edge of Atom-en, Kashima area, Matsue city on 5 January 2011. The aim of this study is to clarify the mechanism of the landslide. Three main works were carried out. Field survey was conducted to observe the structure of the landslide and measure the in situ shear strength of the soil on the sliding surface. Laboratory test was conducted to obtain soil strength properties such as permeability and shear strength. Finally, back analysis using Janbu’s method was conducted to obtain the shear resistance of the sliding mass in the lower part of the slope, and to evaluate the effect of rise in groundwater level, while Flac3D software program was used to clarify the deformation process of the landslide. The investigation and analysis indicated that the slope behind Atom-en has complex geologic structure, composed of completely weathered tuff and shale. The unfavorable geological structure and condition were the inherent factors that contributed to the landslide occurrence, while snow melting was the main triggering factor.