PURPOSE: To facilitate works by attaching a joining end plate to the end of a steel pipe column, and piling up the mutually joined end plates at the end of the column and bolt-joining them.

CONSTITUTION: A circular end plate 2 being the same in diameter as the outer diameter of a column 1 is previously welded to the end of the column 1 composed of a circular steel pipe whose ends are mutually joined for mutually attaching them in one body. The end plate 2 is previously formed with a plurality of bolt holes, and a notch 4 and a window hole 5 are formed on the end of the column 1 so as to correspond to the bolt hole. Next, a bolt 6 is inserted into the bolt hole through the window hole 5, and a nut 7 is threadedly engaged with the bolt 6 and tightened for mutually joining the end plates 2. Thus the fastening work through the window hole can be facilitated.