Recently, automobile features designed to improve maneuverability and convenience are being improved. However, many drivers still have difficulty with parking maneuvers. Although parking is unavoidable for drivers, yet ranks third among the most difficult driving situations for Japanese drivers. Drivers in other countries also consider parking to be difficult and even skill drivers would appreciate some assistance. Therefore, a parking support system has been developed to reduce the workload for all drivers while also improving parking performance.The parking support system Human-Machine Interface (HMI) operation should be designed to easy to use for best performance. The back-in perpendicular parking performance of drivers with different skill levels was studied to see the effect of the parking support system. Back-in perpendicular parking is the major parking method in Japan. Two prototype systems were developed to investigate their effectiveness on their mental load reduction using the NASA-TLX. The results show that one parking support system works effectively for mental load reduction while the other does not.