The field surveys were carried out to know the characteristics of sediment movement phenomena in the volcanically disturbed area after the 2000 eruption of Usu Volcano. As a result of the surveys, a sediment budget was made quantitatively for the area. Comparing to the past studies, a significantly large value of erosion rate was obtained, where 180 mm/yr for surface erosion and 53 mm/yr for gully erosion. The reasons can be considered as follows. 1) The surface fine-ash layer was thick enough not to stop the erosion because of the exposure of the underlying permeable layer. 2) The precise quantification of the amount of the deposition and the gully erosion enables us to estimate the erosion rate for the period from the real beginning.