A 54-year-old man suffering from muscle weakness in his lower limbs was admitted to our hospital for further diagnosis and rehabilitation. He was seen to have remarkable muscle weakness and atrophy in the bilateral triceps surae muscles without any sensory deficit. EMG revealed polyphasic MUPs and normal MCVs and SCV. He was able to walk but unable to keep his balance while standing, and on questioning it was found that his father, uncle and elder brothers had the same symptoms. Therefore, he was diagnosed as having familial spinal progressive muscular atrophy, and we thought that this strange symptom was astasia without abasia or stilts phenomenon. We made two plastic AFOs, a shoe horn brace and a KU half AFO, to resist ankle dorsiflexion during the stance phase. The AFOs improved his static standing balance, which was evaluated by Kistler's force plate, and the efficacy of walking, which was evaluated by the Physiological Cost Index. As the shoe horn brace was more effective for determining the Physiological Cost Index and subjectively better than a KU half AFO, we selected the shoe horn brace for the treatment of his stilts phenomenon. We concluded that the shoe horn brace resisting ankle dorsiflexion during the stance phase was able to improve the stilts phenomenon.