To provide a steel pipe column of an external diaphragm type having a sufficient resisting force against an applied stress from a beam at a column-beam joint part, and having excellent transportation efficiency and handling performance upon construction since a projection part is small.

The square steel pipe column 2 of the external diaphragm 1 type has an external diaphragm 1 at a column-beam joint part. The external diaphragm 1 is capable of orthogonally joining H-shaped cross-section beams. The projection width Hd of the external diaphragm 1 with respect to an outer diameter D of the steel pipe satisfies the formula of Hd=0.15D to 0.4D. The cross sectional area Ad (=projection width Hd×board thickness td) of the external diaphragm 1 is the area that can bear, with the shear resistance, the applied stress from the H-shaped cross-section beams which are to be joined.