Prevention and reduction of medical accidents is essential. Among medical accidents, accidental falls remain a serious problem. While "assessment score sheets" have already been used in hospitals to prevent accidental falls, satisfactory results have not actually been achieved. In this study, we aim to establish a methodology for preventing accidental falls. We consider that the 'management plan' for each patient includes three factors. A plan of instructions for patients on actions they can take for safety in their ADL (Activities of Daily Living) is essential as a base. Second, a plan to keep up with any short term change in a patient's state is needed, because the state of a hospitalized patient will usually be temporarily affected by medication and changing medical conditions. We develop a model for preventing accidental falls, which enable us to design appropriate management plan for each patient. Then, we develop a prototype system based on the designed model. Finally, we address the result of verification of the model, by applying the prototype system into actual cases in hospitals.