An improvement in a continuous process for the relaxing heat treatment of crimpable filaments, particularly potentially crimpable filaments which comprises passing the filaments overfed from a filament charging apparatus through an ejecter, wherein a heated fluid is ejected, to subject the filaments to pre-heating and fiber separation, spraying a heated fluid onto the filaments at right angles from their circumference in a low tension zone under a tension as low as 1 mg/denier or less to subject the filaments to relaxing heat treatment, and then passing the treated filaments through a heat treatment chamber to subject the filaments to thermal setting, and an apparatus therefor.