To provide a technology capable of manufacturing an electric resistance welded tube having excellent welding quality, grooving corrosion resistance and workability of a tube joint with high productivity by the hot or warm finish.

The electric resistance welded tube 8 is manufactured by heating a steel strip 2 by a steel strip heating furnace 3, and performing the forming and electric resistance welding by a forming and induction heating welding equipment 4 to manufacture a steel tube. After the steel tube is re-heated continuously by a tube re-heating device 5, the steel tube is reduced by a reduction mill 6, and further cut to a predetermined tube length by a tube cutter 7 to manufacture the electric resistance welded tube 8. If the finish temperature of the reduction is set to be ≥Ar3 point, and, in particular, if C content is ≤0.2% or ≥0.001% to ≤0.2%, the finish temperature of the reduction is set to be ≥(Ar3 transformation point -50°C), and the aspect ratio of a main phase structure of the electric resistance welded tube 8 is set to be ≤5.0 by setting the starting temperature of the reduction to be higher than the finish temperature by 50°C.