In this paper, a novel, low-cost lower extremity gait rehabilitation device using a single actuator is presented. The proposed device is based on a single DOF 8-bar Jansen mechanism, which was recently introduced as an efficient walking mechanism for legged robots. The mechanism is synthesized to generate the ankle trajectory during human gait relative to the hip, in terms of both position and time. Two mechanisms, one for each lower limb, are applied reciprocally and mechanically synchronized to guarantee symmetric gait. A custom designed seat-type weight support system is also introduced. It supports weight of the user and mechanisms, and also provides the required interaction while maintaining mobility at the hip. To accommodate different users, several parameters of the mechanism are adjustable. Ease of donning-doffing action, weight-bearing and possibility of unhindered arm swing have been considered to provide an effective and user-friendly training environment. A prototype is manufactured, and a pilot study with a healthy subject is conducted to demonstrate feasibility of the concept. Due to ease of control, cost-effectiveness and high intrinsic safety, the proposed system potentially offers a possible method of gait training.