PURPOSE: To improve the quality of a 13 chromium martensite type stainless steel bent tube used as a pipe joint in piping for sour oil wells, sweet oil wells, etc., and to secure high strength while moderately reducing hardness and improving ductility and toughness.

CONSTITUTION: As heat treatment following high-frequency bending, after bending in a temperature range of Ac3 or higher (about 950 to 1050°C) or at about 800°C, quenching by rapidly cooling while keeping the temperature within 800 to 850°C and the tempering by keeping the temperature at 700 to 750°C are carried out. When bending is carried out at about 800°C, quality is fully improved only by heat treating by keeping the temperature at 700 to 750°C followed by air cooling instead of the above-mentioned quenching and tempering.