Abstract: The invention resides in enabling biodegradable filament of polylactic acid, polyglycolic acid and the like to manufacture biodegradable micro-filament by simple and convenient means without needing special, high-accuracy and high-level apparatus; it is characterized in that highly molecular oriented micro-filament those of 12 ?m or less and generally from 2 ?m to 3 ?m can be obtained by heating biodegradable filament by infrared beam and the heated original filament is drawn to 100 times or more by tension of 10 MPa or less.