PURPOSE: To enhance the construction efficiency by dividing an elevated structure into a plurality of parts in the peripheral direction, ground-assembling the structure respectively as a divided unit, directly connecting a tension material for automatically narrowing a space according to a lift up and hoisting the structure by a lift up device.

CONSTITUTION: An observation room 14 is divided into a plurality of parts in the peripheral direction, previously built on the ground as respective divided units 14a... and distributively arranged with an almost equal space l in the periphery of a leg part of a tower body 12 to connect upper and lower end parts between the divided units 14a respectively by a tension material 16. The tension material 16 is formed of a rope or a wire and rewound by a predetermined proportion according to a lift up of the unit 14a through an automatic rewinding machine or the like, mounted to each each unit, to decrease the space l. The units 14a are lifted up all together through a lift up device 20 and fixed to the tower body 12 by connecting hanging rods 18 to body end parts in an upper surface of the unit 14a. In this way, the construction period can be shortened by improving the workability.