Allowable sediment discharge is the sediment discharge wich is allowed to flow downstream through an outlet of an area conducted Sabo works. And the ifference between planned sediment discharge and the allowable sediment discharge is considered the sediment which should be checked with sediment control (sabo) structures such as sabo dams. Allowable sediment dischare has been defined differently by different persons. It, however, has not been explained clearly. Some river bed sediment discharge under various conditions, flood peak discharge, bed material size, sediment supply through the upstream end of an alluvial fan. It was made clear that; (1) It is possible to estimate allowable sediment discharge with the technique shown here. (2) Bed material size used in the calculation affects the result markedly. As the bed material size is expected to be smaller during large floods new landslides, debris flows and bank erosion. It is necessary to sample transported bed material during and just after floods.