To stably perform stretch-breaking while random stretch-breaking property is maintained even in a low humidity by combining filament yarns treated with a finishing oil which is solid at normal temperature under the absolute dry condition with filament yarns treated with a finishing oil which is liquid at normal temperature under the absolute dry condition.

Filament yarns treated with a finishing oil which is solid at normal temperature under the absolute dry condition are combined with filament yarns treated with a finishing oil which is liquid at normal temperature under the absolute dry condition and the combined yarns are subjected to stretch- breaking. In the system, convergent property can be kept while the random stretch-breaking property is maintained even in low humidity and uniform spun- like finished yarns are obtained in high operability.