Capabilities to locate damage, and applicability to simply supported bridges are considered as basic characteristics of the method to be investigated in this paper. A new method which employs support reaction and mid-span displacement as indicators is presented to detect a certain type of damage. Unlike the existing study, this work proposes the direct relationship between the change in local mass caused by damage and the measured support reaction and mid-span displacement values. With the cooperation of inspection means, this method is capable of successfully identifying the location of local potential damage. The feasibility of this method is demonstrated by numerical simulation and model experiment.