The impact force is measured usually by the method of Hopkinson Pressure Bar. However, the measurable time range of this method is restricted by the length of the bar. The author suggests a usefull measuring method based on the theory of propagation of longitudinal elastic stress wave. In this method, the external force, ranging from quasi-static to impact, at the end of a cylindrical bar can be estimated by measuring stresses at two suitable points on it. Also the length of the measuring bar can be shorter than in another methods.