A polyester resin composition including 97.0 mass% to 99.9 mass% of a polyester resin (A) and 0.1 mass % to 3.0 mass% of a polycarbodiimide (B), wherein dicarboxylic acid constituent units in the polyester resin (A) include terephthalic acid units and/or 2,6-napthalene dicarboxylic acid units, 5 mol% to 90 mol% of the diol constituent units in the polyester resin (A) are units derived from a diol having a cyclic acetal skeleton represented by formula (1) or formula (2), 0 mol% to 90 mol% of the diol constituent units being units derived from an alicyclic diol, and the polycarbodiimide (B) having two or more carbodiimide groups in each molecule thereof. (In formula (1), R1 and R2 each independently represent a C1-10 aliphatic group, a C3-10 alicyclic group, or a C6-10 aromatic group.) (In formula (2), R1 is the same as in formula (1), and R3 represents a C1-10 aliphatic group, a C3-10 alicyclic group, or a C6-10 aromatic group.)
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