A steel mother pipe obtained by a solid phase butt-welding pipe-making process or a welding pipe-making process is reduced by heating the pipe prior to the reduction at a temperature exceeding 100.degree. C. and lower than 800.degree. C. wherein the temperature of the steel pipe being reduced is controlled within a defined range. The temperature difference along the circumferential direction of the mother pipe at the inlet side of a reducer is within a defined range, and the temperature of the steel pipe at interstand positions of the reducer is also controlled. By virtue of this control, the reduction becomes possible at low load while suppressing work hardening without degrading surface properties. The resultant product pipe has a dimensional accuracy maintained at a high level.