A polyester film for sealant use comprising a polyester resin having ethylene terephthalate as a main structural component and including one or more monomer components that may serve as amorphous components so that the total amount of the monomer components being not less than 15 mol% and not more than 30 mol% among total monomer components, wherein the monomer components are at least one selected from the group of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol and hexanediol, and wherein, the polyester film is uniaxially or biaxially stretched and satisfies the following requirements to : the heat-sealing strength is not less than 2 N/15 mm and not more than 20 N/15 mm when the polyester films are heat-sealed to each other at 130°C; the heat-sealing strength is not less than 2 N/15 mm and not more than 8 N/15 mm when the polyester film is heat-sealed to other biaxially stretched polyester film formed of a crystalline polyester at 130°C; the heat-sealing strength is not less than 2 N/15 mm and not more than 20 N/15 mm when the polyester film is heat-sealed to other unstretched polyester film formed of a crystalline polyester at 130°C, wherein said heat-sealing strength referred to in , and is determined as indicated in the description; and the crystal melting heat capacity ΔHm measured by differential scanning calorimetry (DSC) as indicated in the description, is not less than 10 (J/g) and not more than 40 (J/g). a polyester resin having ethylene terephthalate as a main structural component and including one or more monomer components that may serve as amorphous components so that the total amount of the monomer components being not less than 15 mol% and not more than 30 mol% among total monomer components, wherein the monomer components are at least one selected from the group of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol and hexanediol, and wherein, the polyester film is uniaxially or biaxially stretched and satisfies the following requirements to : the heat-sealing strength is not less than 2 N/15 mm and not more than 20 N/15 mm when the polyester films are heat-sealed to each other at 130°C; the heat-sealing strength is not less than 2 N/15 mm and not more than 8 N/15 mm when the polyester film is heat-sealed to other biaxially stretched polyester film formed of a crystalline polyester at 130°C; the heat-sealing strength is not less than 2 N/15 mm and not more than 20 N/15 mm when the polyester film is heat-sealed to other unstretched polyester film formed of a crystalline polyester at 130°C, wherein said heat-sealing strength referred to in , and is determined as indicated in the description; and the crystal melting heat capacity ΔHm measured by differential scanning calorimetry (DSC) as indicated in the description, is not less than 10 (J/g) and not more than 40 (J/g). <EOS>