The prediction expreiments of debris flow occurrence with flooding in Mizunashi river are made using the rain score predicted by the 1-3 hour rainfall forecasting method. The results show the usefulness of rain score P information for the precaution activity of inhabitants against the damage. They have sufficient time of 20-30 minutes for escaping from debris flow hazard in all cases tested, if the precaution activity is started at the time when the predicted P is crossing the criterion P≧-5 with 62.5% probability of debris flow occurrence or P≧0 with 75% probability.