NOVELTY - A biaxially-stretched polyester film comprises polyethylene terephthalate resin. The film haze variation (haze after heating at 170 degrees C for 20 minutes-haze before heating) is less than 1, the amount of terminal hydroxyl group is 70 eq/ton or less, the cyclic trimer content is 0.45 %mass or less, the thickness is 30-50 mu m, the plane orientation degree is 0.15-0.18, and the ratio of front and/or back surface axis orientation degree is 0.8-0.98.    USE - Biaxially-stretched polyester film is used for curable-resin laminates (claimed) e.g. reflecting plates, diffusion sheets, lens sheets, hard coat films of LCD devices, and other optical films. Can also be used for touch panels, protective films of solar cells, solar-cell backsheets, polarizing-plate protective films, organic electroluminescent elements, electronic paper, recording materials, and building materials.    ADVANTAGE - The biaxially-stretched polyester film has reduced heating whitening, and excellent planarity, transparency after heating, mechanical strength, chemical resistance, and heat resistance. Precipitation of oligomer and cyclic trimer is reduced. Post-processing at high temperature is possible. Since contamination during film formation is reduced, film defects are reduced.    DETAILED DESCRIPTION - A biaxially-stretched polyester film comprises polyethylene terephthalate resin. The film haze variation (haze after heating at 170 degrees C for 20 minutes-haze before heating) is less than 1, the amount of terminal hydroxyl group is 70 eq/ton or less, the cyclic trimer content is 0.45 %mass or less, the thickness is 30-50 mu m, the plane orientation degree is 0.15-0.18, and the ratio of front and/or back surface axis orientation degree is 0.8-0.98. The front and/or back surface axis orientation degree is calculated as follows. The light absorbency (A) at a wavelength of 1340 cm-1 and the light absorbency (B) at a wavelength of 1410 cm-1 are calculated by polarization attenuated total reflection (ATR) method with respect to a film sample. The ratio (Y = A/B) is calculated. With the point as starting point measured initially, in-plane rotation is carried out every 10 degrees , and the film sample is measured similarly at 0-170 degrees . The maximum or minimum value in 18 acquired points is set as surface axis orientation degree (Ymax or Ymin). The surface axis orientation degree is measured on the front and back of film sample. The ratio of Ymax and Ymin is then calculated by making the larger value the denominator. INDEPENDENT CLAIMS are included for the following:    (1) curable-resin laminate consisting of a curable-resin layer and the biaxially-stretched polyester film as base film; and    (2) manufacture of polyethylene terephthalate film, which involves using polyethylene terephthalate resin which is heat-processed as follows. A humidity-controlled inert gas having a water content of 3.5-30 g/Nm3 is circulated at a flow volume of 1-10000 l/kg crude polyester having an intrinsic viscosity of 0.5-0.7 dl/g obtained by polycondensation of dicarboxylic acid component and glycol component, per hour, and the polyester is heat-processed at 190-260 degrees C. Heat-processing is further carried out such that the change (intrinsic viscosity before heat processing-intrinsic viscosity after heat processing) in intrinsic viscosity of polyester is -0.05 dl/g to 0.05 dl/g.