A large number of debris flows occurred in the northwestern part of Hiroshima Prefecture on July 21st in 1988. On the basis of the survey data and the result of analysis on the type of valley in topographic maps and comparison between the contour lines in topographic maps and summit level maps, we explained that the landslides on concave landform occurred easily on steep and undissected valleys and the failures of side slope and waterside tended to occur on dissected valleys. Moreover the courses of debris flows agree well with those that we estimated by the topographic analysis. The method with the topographic analysis in this report could be utilized to make a hazard map for the prevention of debris flow disasters.