In recent years, with application to soft ground with poor conditions in mind, the development of techniques to build foundation types using spiral piles has been progressing. However, there have been few examples of experiments conducted under strict control and conditions closer to real phenomena. Therefore, in this study, we performed a scale-similar model experiment that reproduced the stress state of the actual scale ground by loading the seepage force and clarified the vertical bearing capacity characteristics of the spiral pile in the saturated sandy ground. This paper reports the results of penetration and vertical loading experiments on the saturated ground using straight and spiral piles. The experiment results clarify the differences in the support mechanisms of the two types of piles in a full-scale saturated ground.