Provided are a polyester-based adhesive layer, adhesive tape, and double-sided adhesive tape having excellent durability (storability in warm, humid conditions) and adhesive characteristics through use of a polyester-based adhesive composition. This polyester-based adhesive composition contains polyester, a hydrolysis-resistant agent, a tackifier, and a crosslinking agent, and is characterized in that the acid value of the tackifier is 8 or less, the softening point of the tackifier is 80-170 DEGC, and the content of the tackifier with respect to 100 parts by weight of the polyester is 20-100 parts by weight.