Although the environmental adaptability of walking is very high, its efficiency is poor because of the deadweight torque that supports the body weight. In particular, this torque places a substantial load on the leg muscles of workers that carry heavy objects or stand for long durations. Most research on methods for assisting deadweight torque with machines focuses on those that use electricity to implement both interlocking and assistive power. Our research focused on the development of a lightweight assistive device powered solely by the recovery of the potential energy of the upper body that is lost while walking. This system uses surge tanks, three-way valves, and other features in a simple configuration. In addition, the system is interlocked with walking by switching between assisting the swing leg and assisting the contact leg using a simple sensing system. This paper examines the theoretical basis for the potential energy regeneration system and presents the results of tests using a prototype worn by walkers at speeds of 2-5 km/h.