In recent years, climate change has resulted in frequent damage due to excessive sediment inflow. However, the effects of changes in upstream and downstream gradients and associated changes in sediment supply in river channels are still unknown. In this study, we attempted to understand the channel deformation in the place where the gradient and sediment supply change by using the movable bed experiments and numerical simulations. As a result, (1) in a place where the amount of sediment supply is large, although the range of influence is limited, the left and right riverbanks are widely eroded because the alluvial fan-shaped sediment accumulation promotes the branching of the channel. (2) In a place where the sediment supply decreases, the erosion of one bank is predominant and the channel meanders because the branching of the channel is suppressed as the riverbed lowers. (3) When the sediment supply is close to equilibrium, the channel is divided appropriately and the left and right banks are eroded almost evenly, so the maximum amplitude of the channel is smaller than the above two fields.