This paper is about walking assist control for an exoskeleton. Wearing an exoskeleton, the wearer can be helped in heavy work or remaining in a fixed posture for long periods. Therefore, exoskeletons are expected to use in industry, medical welfare, farming, logistics, and so on. Numerous effective exoskeletons have been proposed. However, there are few products which have brought on the market. In this paper, a lower-limb assistive exoskeleton for mainly agricultural use is developed. Two motors on the both hip joints and free knee joints, assist not only thigh but also leg region. The concept of passive dynamic walking is partly used in mechanism and control method to realize this objective. Passive dynamic walking might be said to be an ideal bipedal walking form. Also a power assisting controller based on virtual gravity force method and delayed feedback control is proposed．Experiments show good effects of assisting lower-limb indirectly.