To search for warm-hot intergalactic medium (WHIM), a small satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyer) is planned and a specially designed four-stage X-ray telescope (FXT) has been developed as the best fit optics to have a wide field of view and a large effective area. Based on the previous works such as the design of optics and replica foil mirror fabrication, we made the demonstration model of the FXT, which has a set of four-stage mirror supported by alignment plates to reduce alignment errors between different stages. On the selection of mirror surface metrial, we tried to increase the reflectivity of gold or platinum replica mirror at low energies. We are also trying to make Ni replica mandrel having the shape of four different cone angles for developing a full or partial shell of four-stage mirror formed in a same substrate. We describe the expected performance and alignment procedure of the demonstration model, the present status of the selection of mirror surface material and the development of Ni mandrel.