To manufacture a steel tube having an excellent seam quality and a surface skin with high productivity.
A band steel is preheated and continuously formed by a forming roll group to obtain an open tube 7. Both edge parts of the open tube 7 is subjected to edge preheating 4 heating to Curie point or over, preferably less than 1300°C by an induction heating and further subjected to the edge heating treatment to a temperature area of 1300°C or over and less than a melting point by either one 5 of laser beam, electronic beam or plasma beam, then abutted on each other by a squeeze roll 6 and press-weld to obtain the steel tube. It is preferable that the time tK (sec) keeping joint part at 1300°C or over after press-welding is 0.03sec or over, or the joint part is kept for the time according to an oxygen concentration in an atmosphere. Further, it is preferable that the preheating of the band steel is performed at 800°C or below, the edge preheating, the edge heating, and the press-welding is performed in an atmosphere with an oxygen concentration lower than the atmosphere or in an atmosphere whose dew point is -10°C or below.
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