As a method of detecting bridge damages at low cost, the applicability of VRA (Vehicle Response Analysis) based on SSMA (Spatial Singular Mode Angle) has been examined. The previous studies for SSMA-based method numerically and experimentally shows that SSMA is a sensitive index for serious damages. However, for practical application of this technology, it is necessary to detect not only serious but also relatively mild damages. In this study, to examine the applicability of SSMA-based method to the detection of mild damages, an actual sensor-equipped car travels on a steel girder bridge. Bolts are loosened, and a lateral girder is removed as the damage models. As the result of this experiment, it is found that both damages can be detected by the Maharanobis distance of SSMA.