Polyester-based sealant film and packaging using same

To provide a polyester-based sealant film used for layering a gas barrier layer, to which the adsorption of components from the contents is small, which has high heat-sealing strength in low-temperature regions, which does not decrease gas barrier properties in a step such as a vapor deposition step for providing a gas barrier layer, and that allows the gas barrier layer to have excellent gas barrier properties. The polyester-based sealant film is characterized by meeting the requirements (1) to (4), and having at least one heat-seal layer, the heat-seal layer being formed from a polyester having ethylene terephthalate as the main component. (1) When heat-seal layers are sealed to one another for 2 seconds at 140 DEG C and 0.2 MPa, the seal strength is 5 N/15 mm to 10 N/15 mm inclusive per 10 [mu]m film thickness. (2) When the temperature is raised from 30 DEG C to 220 DEG C at 10 DEG C/minute during thermomechanical analysis (TMA), the maximum thermal shrinkage is 1% to 12% in at least one of the length dire