In recent years the number of vehicles equipped with millimeter wave radar has been increasing due to the popularization of driving assistance systems such as adaptive cruise control (ACC) and forward vehicle collision warning (FCW) systems. Consequently, high performance millimeter wave radar must be developed to support even more advanced driving assistance systems. The investigation described in this paper confirms that it is possible to use high range resolution radar to recognize the width of a target. In tests, a simulated radar signal was transmitted and received by a millimeter waveband network analyzer using a 1.6 meter-wide aluminum foil board as the target. When the range resolution was low, only one point of reflection from the board could be detected. However, when the range resolution was improved, then multiple points of reflection from the target could be detected. The high range resolution radar improves the separation performance of the target and also improves the detection performance of close range targets. In addition, the results of the tests indicate that the high range resolution radar contributes to recognizing the width of the target by grouping together the multiple detected points.