The Yoshino River, Japan, is rich in water resources, but simultaneously possesses high risk of flood disaster. River improvement works to reduce damage from the floods have been conducted which attain increase of the discharge capacity. On the other hand, local sediment deposition and scouring are growing concern by the repeated floods, decreasing of sediment supply and construction of river structure. In order to resolve these problems, it is necessary to understand the effects of natural and artificial impacts on the river channel. In this paper, the channel transition processes were studied in the Middle Yoshino River using aerial photo, morphology data. Natural and artificial impacts on those processes were evaluated from sandbar deformation, fluctuation of bed elevation and volume in low-water channel. As a result, sandbar deformation by the floods and revetment works was confirmed. The floods and dam construction affected fluctuation of river channel with the sediment deposition and scouring.