NOVELTY - A biaxially-oriented polyester film comprises layers of polyester (A) laminated with greater than or equal to 50 layers of layers which use polyester (B) on thickness direction in which (1) greater than or equal to 55 mol.% total of glycol unit in film is structural unit derived from 1,4-butanediol, and greater than or equal to 55 mol.% total of dicarboxylic acid unit in film is structural unit derived from terephthalic acid, and (2) greater than or equal to 60 mol.% total of glycol unit of polyesters (A) and (B) is structural unit derived from 1,4-butanediol, and greater than or equal to 40 mol.% total of dicarboxylic acid unit of polyesters (A) and (B) is structural unit derived from terephthalic acid.    USE - A biaxially-oriented polyester film for battery exterior and pharmaceutical packaging (all claimed).    ADVANTAGE - The biaxially-oriented polyester film has excellent moldability and curvature-proof property after molding by adjusting the mechanical strength of polyester.    DETAILED DESCRIPTION - A biaxially-oriented polyester film comprises layers of polyester (A) laminated with greater than or equal to 50 layers of layers which use polyester (B) on the thickness direction in which the film satisfies the following requirements: (1) greater than or equal to 55 mol.% total of glycol unit in the film is structural unit derived from 1,4-butanediol, and greater than or equal to 55 mol.% total of dicarboxylic acid unit in the film is structural unit derived from terephthalic acid; (2) greater than or equal to 60 mol.% total of glycol unit of polyester (A) and polyester (B) is structural unit derived from 1,4-butanediol, and greater than or equal to 40 mol.% total of dicarboxylic acid unit of polyester (A) and polyester (B) is structural unit derived from terephthalic acid; and (3) reflectance of wavelength 350-2100 nm region is less than or equal to 25%.    DESCRIPTION OF DRAWING(S) - The drawing shows a graph of the elongation curve obtained by the tension test of a film. (Drawing includes non-English language text).