We are developing a passive power-assist supporter called Smart Suit Lite, which is a compact and lightweight power-assist device that utilizes the restoring force of elastic belts. Smart Suit Lite is designed not only to support muscles but also to stabilize the torso similarly to a corset. However, because a corset is always tight around the waist, negative effects caused by long-term use has been pointed out. In contrast, the tightening force generated by Smart Suit Lite increases only when the wearer adopts a posture corresponding to higher load on the low back. In this research, we performed two basic experiments to evaluate the static balance ability of wearers. As a result, the standard deviation of the lumbar angle decreased by 32.1% on average in wearers with low stability.