PURPOSE: To minimize a welding width, to improve corrosion resistance and fitness and to reduce cost by moving a timepiece band formed of a spiral member while varying the speed of a light source of an optothermal means, then moving the optothermal source in the opposite direction thereby welding the longitudinal end of the band.

CONSTITUTION: A band body 19 is set on a welding jig base 18 and welding is started from a guide plate a16 side by a torch 20. The torch 20 is then moved at the torch speed exceeding the weldable speed from the mid-way in the transverse direction of the band so that the torch is passed along a guide plate b17. The moving direction of the torch 20 is thereafter made opposite and the welding is executed at the first torch speed. The band which is welded at the min. required width P of the weld zone 11 and is minimized with the uneven width P is thus obtd.