A huge flood attacked the Saru River basin、 which locates at Hokkaido in Japan、 in August of 2003. The flood generated large amounts of driftwood and many bridges were damaged by the flow and the drift woods.Based on an onsite survey conducted immediately after the flood、 we examined the driftwood in the Saru River. We studied the distribution of locations where driftwood beached in the river channel、 the volume of such driftwood、 the distribution of driftwood origin in the river channel、 reasons for driftwood originating there. The influence of driftwood to the rivers structures (bridge piers etc) is also investigated. It became clear that the driftwood generated from the river channel and the mountain area occupied 20% and 40% of all driftwood、 respectively as a result of investigation.