To provide a thermally shrinkable polyester-based film for the full labels of bottles, which little forms shrinkage wrinkles, shrinkage irregularity and strains, and has a light-shielding property, even when not printed or processed.

This thermally shrinkable polyester-based film whose thermal shrinkage rate is 50 to 80 % at a treating temperature of 98°C for a treating time of 10 seconds in the main shrinkage direction and is ≤10 % at a treating temperature of 98°C for a treating time of 10 seconds in the direction orthogonal to the main shrinkage direction is characterized by having a total light transmittance of ≤25 %, a whiteness degree of ≥85 %, and a 800 nm wavelength light transmittance of <5 %.