To eliminate a problem of high cost required when high-altitude scaffolding for a building is built up from the ground, a problem of high cost and a complicated procedure posed when a tower vehicle is employed, and a problem of absence of a suitable indoor column or the like in some cases, at the time of using a bracket extending out of a window with the aid of the column or the like, and to provide a method for more easily building the scaffolding.

There is provided a basal instrument for mounting the scaffolding at high altitudes, which has a plurality of foot holding portions 1 like a ladder, and mutually opposed leg-like frame bodies which are foldingly arranging in parallel with each other across a length which exceeds the width of a window sill 2 after opening a window of the building. At least one of the leg-like frame bodies exceeds the height of the window sill 2 and forms an outside-window frame body 3. Then, the outside-window frame body 3 has a scaffolding mounting portion 5 at a lower end thereof, on which a scaffolding elevator 4 is mounted. The other leg-like frame body forms an indoor leg-like frame body 7 which is provided with a squeezing means 6 for pinching the window sill 2 at least at one portion thereof. There is also provided a method for building the scaffolding.