A double-action hydraulic forming simulator (“Simulator”) has been designed to investigate sheet forming processes accurately and systematically. The new machine allows precise control of several process variables. In this study, the Simulator and new scale-model fender dies have been employed for experiments to evaluate the effects of the Blank Holding Force (BHF) control in sheet forming. By the experimental approach, it has been made clear that quality defects of panels formed by stamping processes, such as wrinkles, surface distortion, and fracture, can be suppressed by increasing or decreasing the BHF during the operation. The two simple BHF control patterns, the increasing method and the decreasing method, are effective enough to improve the quality of products and are practical for industrial application.