This paper proposes a wearable chair that reduces the burden on the lower limbs in standing and details the orthosis we developed. The wearable chair consists of a seat, thigh link, lower thigh link and a pair of shoes. These components are connected by pneumatic passive elements and switched from free motion to fixed position by vacuum pressure. Users can sit at any place or time by fixing the joints. The pneumatic passive elements are flexible and lightweight compared to conventional passive device. Results of experiments on walking and weight support using the chair are described.