A polyester film having at least 15% thermal shrinkage at 150 DEG C in the primary shrinkage direction, less than 15% thermal shrinkage at 150 DEG C in a direction orthogonal to the primary shrinkagedirection, and no more than 14% thermal shrinkage at 90 DEG C in the primary shrinkage direction; and a polyester film having at least 15% thermal shrinkage at 150 DEG C in the primary shrinkage direction, less than 15% thermal shrinkage at 150 DEG C in a direction orthogonal to the primary shrinkage direction, and a glass transition temperature of at least 100 DEG C obtained by temperature-modulated DSC. A polyester film having little or no shrinkage at 90 DEG C being the processing temperature for the coating step and drying step, etc., and having great shrinkage at the shrinkage step temperature.