Presently electric locomotives and electric multiple units are designed by assuming high adhesion performance. However, they often cause problems of slip and slide of wheels. We developed a "Vehicle Traction Tester" to facilitate the analysis of wheel slip and slide and other phenomena at running performance tests. A.C. traction motor currents always vary to make it impossible to grasp the instantaneous current vector from one-phase current as is usually measured. We introduced a "Vector Calculator" that uses two-phase currents so that we can see the instantaneous amplitude and phase of the current vector. Furthermore, we developed a new "Train Running Resistance Analyzer" that shows running resistance on a display on a real time basis and makes statistical data processing faster and easier.