Disclosed is a highly adhesive polyester film having a highly adhesive primer layer disposed on at least one side of a substrate polyester film. The substrate polyester film is a stretched film having linear tearability and formed of a mixed polyester resin containing polyethylene terephthalate and a modified polybutylene terephthalate, and the highly adhesive primer layer contains a polyester resin (A) having an acid number of 20 to 60 mg KOH/g and a hydroxyl number of 30 to 150 mg KOH/g, and having an oligomer content of 2.0% by mass or less, and substantially contains no crosslinking agent component.