NOVELTY - A biaxially oriented polyester film comprises polyester resin composition containing carbon black particles, and in which the flame retardant agent or a dispersant is not contained in the polyester resin composition that constitutes the film, and has optical density of 3.5 or more, and the flame retardancy of VTM-0, VTM-1 or VTM-2. The flame-retardant evaluation method involves sample preparation, measurement method and flame-retardant evaluation, in which VTM-0, VTM-1, and VTM-2 satisfies preset criterions.    USE - Biaxially-oriented polyester film is used for light-shielding component of optical apparatus and solar cell back sheets (all claimed).    ADVANTAGE - The biaxially-oriented polyester film has excellent light-shielding property, concealability, flame retardance and continuous productivity.    DETAILED DESCRIPTION - A biaxially oriented polyester film comprises polyester resin composition containing carbon black particles, and in which the flame retardant agent or a dispersant is not contained in the polyester resin composition that constitutes the film, and has optical density of 3.5 or more, and the flame retardancy of VTM-0, VTM-1 or VTM-2. The flame-retardant evaluation method involves sample preparation in which a measurement sample (biaxially-oriented polyester film) is cut into 20cmx 5cm, and left to stand at 23 degrees C and 50 %RH for 48 hours is set as the sample A, and the sample cooled at 23 degrees C and 20 %RH or less after heating at 70 degrees C and 168-hour leaving-to-stand for 4 hours is set as the sample B, and five samples are each prepared as one set, and measurement method in which a line is drawn from the short side of each sample to a short side and a parallel direction at the place of 125 mm, and it winds around the stick of diameter 12.7 mm so that a short side may become an up-down direction, and after fastening the inside of the 75-mm portion above a 125-mm mark by a pressure sensitive tape, it extracts out a stick. The upper end of the sample is closed so that there may be no chimney effect during a test. Each sample is set vertically and absorbent cotton is placed on 300-mm downward direction. Let the Bunsen burner of the diameter of 9.5 mm, and 20 mm of flame length be a heat source so that the pipe of a burner is located in the place of 10 mm from the lower end of a sample and the indirect flame of the blue flame is carried out in the center of the lower end of a sample for 3 second, the burning time (t1) after flame separation of the 1st time is measured. Immediately after a flame then, disappears, an indirect flame is again carried out for 3 second, and the burning time (t2) and fire source time (t3) after flame separation of the 2nd time are measured. Any combustion which blazes up to a 125-mm mark exists and observation of whether there existed any combustion falling component to which absorbent cotton is lit are also performed in the case of the flame contact of the time (T1) and the time (T2). The measurement is performed to each one set of sample A and sample B, and flame-retardant evaluation in which flame retardance is evaluated in which in VTM-0, both criterion (A), (I) (U) (E) and (O) are satisfied, in VTM-1, both criterion (A'), (I') (U') (E) and (O) are satisfied, in VTM-2, both criterion (A') (I') (U') and (E) are satisfied, and in VTM absence, it does not correspond any of VTM-0, VTM-1, and VTM-2, in which the criterion (A) of all sample, the longer one is 10 second or less among the burning time (t1) after flame separation of the time (T1), or the burning time (t2) after flame separation of the time, and in criterion (A') of all sample, the longer one is 30 seconds or less among the burning time (t1) after flame separation, or the burning time (t2) after flame separation, criterion (I) which is sum total of the burning time (t1+t2) after flame separation of 5 sheet sample, of the burning time after flame separation per set is 50 seconds or less both the sample A and the sample B, criterion (I') in which is sum total of the burning time (t1+t2) after flame separation of 5 sheet sample, of the burning time after flame separation per set is 250 seconds or less both the sample A and the sample B, criterion (U) of all sample in which sum total of the burning time (t2) after flame separation and fire source time (t3) is 30 seconds or less, and criterion (U') of all sample, in which the sum total of the burning time (t2) after flame separation and fire source time (t3) is 60 seconds or less, criterion (E) of all sample in which combustion or fire source does not reach to a 125-mm mark, and criterion (O) of all sample, in which the absorbent cotton is not lit by fall of the sample which combusted. An INDEPENDENT CLAIM is included for manufacture of biaxially-oriented polyester film.