To provide a polyester film which does not cause troubles such as heat degradation in a vapor deposition step, gives a capacitor having high withstand voltage and insulation resistance properties, and can contribute to the miniaturizing and reliability improvement of a capacitor.

This film contains 0.1-2.0 wt.% fine silica particles obtd. by the high-temp. vapor-phase hydrolysis of a silicon halide and having an average particle size (d50) of 0.1-2.0 μm and has a surface roughness satisfying the formulas: 0.015≤RMS≤0.040, 0.010≤SRa≤0.030, and 0.350≤P-V≤0.600 [wherein RMS is a root mean square roughness (μm); SRa is a central plane mean roughness (μm); and P-V is a max. roughness (μm)].