Method of manufacturing electric resistance welding pipes having excellent characterization of welded seams

A method of efficiently manufacturing electric resistance welding pipes having excellent characterization of welded seams is provided, by which each lateral edge of a rounded strip immediately before electric resistance welding is securely shaped with desired tapering flexibly in response to change in strip thickness, so that welding quality may be kept to be excellent. A method of manufacturing electric resistance welding pipes, in which a strip is subjected to forming, then edges thereof are formed to substantially face each other, and then the edges are subjected to electric resistance welding to form a pipe, wherein an edge and an edge opposed thereto at one of an upper-surface side and a lower-surface side of the strip are shaped with tapering before the forming by means of cutting or shaving, or finpass forming.