PURPOSE: To manufacture a high tensile strength resistance welded steel tube excellent in toughness in the weld zone by subjecting the weld zone of a welded steel tube after the completion of welding to rolling under specified conditions, heating it and allowing it to cool.

CONSTITUTION: A hoop 1 is continuously formed by a roll forming machine 2, and while its joint part is cramped by a squeeze roll stand 4, welding is continuously executed by a resistance welding machine 3. This weld zone (seamed zone) is rolled in the temp. range of ≥400°C at ≥5% draft while bead grinding is executed by a combined bead grinding machine and seamed zone rolling mill 5. After that, it is heated to the temp. range of the Ac3 transformation point to [the Ac3 transformation point+200°C] and is allowed to cool. In this way, the high tensile strength resistance welded steel tube having sufficient strength and low temp. toughness is stably produced on an industrial scale.