To provide an external surface bend measuring-method that enables quantitative measurement of an external surface bend of a steel pipe even in the case of the steep pipe jumping during transportation and that of an elliptical deformation or variation in diameter occurring to the steel pipe, and that allows measurement intervals to be shortened without increasing man-hour.

A method includes: transporting a steep pipe 11 using plural rollers 31 in a longitudinal direction while rotating the pipe in its circumferential direction; arranging three detectors 21 in equidistance between adjacent rollers 31, of the plural rollers 31, the detector for detecting positions of upper and lower ends of the external surface of the steel pipe; calculating the center position of the external surface of the steel pipe from the positions of the upper and lower ends for each of the three detectors, the positions detected by the detectors 21; and calculating a run-out w using the following expression (1). Here, of three detectors 21, CA denotes the center position on an upstream side (A-position), CB denotes the center position at center (B-position), and CC denotes the center position on a downstream side (C-position). w=CB-(CA+CC)/2 ...(1)