Heat-shrinkable polyester-based film and package

A heat-shrinkable polyester-based film comprising ethylene terephthalate units, constituent units derived at least one monomer which forms an amorphous component and constituent units derived from butanediol,

• wherein an amount of the constituent units derived at least one monomer which forms an amorphous component are 18 mol % or more and an amount of the constituent units derived from butanediol are 1 to 25 mol % based on 100 mol % of all polyester resin components,
• wherein the heat-shrinkable polyester-based film satisfies the following requirements (1) to (3):
• (1) the secondary shrinkage ratio of the film is 2% or more and 5% or less when the film is cooled to 25° C. from 100° C. after being primarily shrunk in a chamber kept at 100° C. beforehand;
• (2) the hot-water heat shrinkage ratio of the film in the traverse direction is 10% or more and 30% or less when the film is dipped in hot water at 70° C. for 10 seconds after being aged under an atmosphere at 30° C. and 85% RH for 672 hours;
• and
• (3) the reversing heat capacity difference before and after the glass transition temperature of the film is 0.12 J/g·° C. or more and 0.25 J/g·° C. or less when the reversing heat capacity difference is measured by temperature-modulated DSC.