2 u03bcm draw ratio is 100 times or more and has reached 1 000 time or more even 1 300 times birefringence is 0 015 or more and has reached 0 020 or more even 0 027 at the condition of experiment 4 the un drawn filament filament diameter 207 u03bcm temperature at a melting point 218 u00b0 c tensile strength 0 11 gpa birefringence 0 0013 consisting of a medium density viscosity product viscosity at 240 u00b0 c 3 41 u00d7 1000 pa u00b7 s for original polyglycolic acid was used using this original filament drawing was conducted according to a drawing apparatus and an infrared emitter similar to experiment 4 delivering this original filament at supply speed of 0 5 m min experiments were conducted by changing wind up speed fig1 shows the filament diameters of the drawn filament obtained by the experiment draw ratio calculated from filament diameters and birefringence of the drawn filament from fig1 the filaments diameters are 10 u03bcm or less at appropriate condition and have become thinner to 5 u03bcm draw ratio is 100 times or more and has reached 500 times or more even 1 500 times birefringence is 0 015 or more further 0 020 or more and even has reached 0 026 a filament of filament diameter 1 82 u03bcm and birefringence of 0 056 was obtained by further drawing a drawn filament of 2 5 u03bcm obtained from a method of experiment 4 of the invention at 170 u00b0 c a filament for.