The present invention provides a polyester film, wherein an arbitrary direction on the film surface is defined to have an angle of 0°, and three directions are defined to have angles of 45°, 90°, and 135°, respectively, clockwise from the 0° direction, and the difference between the maximum value and the minimum value of the stresses at 5% elongation in the four directions is 50 MPa or less, the difference between the maximum value and the minimum value of the stresses at 15% elongation in the four directions is 70 MPa or less, and the modulus of elasticity in any one of the four directions falls within a range from 2.0 to 3.5 GPa.