PURPOSE: To stably manufacture a resistance welded tube with a sound welded zone by arranging plural metallic rolls having cooling mechanisms on the insides freely rotatably in a contact state on the periphery of a welding upper roll.

CONSTITUTION: A metallic strip is formed tubularly 3 while being transferred in the longitudinal direction. In the state with both ends thereof abutted on each other, a high-frequency or medium-frequency current is carried to the metallic strip end faces and welding is performed to form the resistance welded tube 3. The welding upper roll 1 to pressurize a welding heating part of the resistance welded tube 3 is cooled. The plural metallic rolls 10 having the cooling mechanisms on the insides are then arranged freely movably in a contact state on the periphery of the welding upper roll 1. By this method, the welding upper roll can be cooled without sprinkling water on the welding roll outside surface.