The polyester resin composition includes: a polyester resin A containing 82 to 88 mass % of a polybutylene terephthalate resin and 12 to 18 mass % of a polyethylene terephthalate resin; a metal organic acid salt B that is either one or both of an alkali metal organic acid salt and an alkaline earth metal organic acid salt; and an inorganic filler C having an average particle diameter of 0.05 to 3 μm in an amount of 1 to 13 parts by mass based on 100 parts by mass of the polyester resin A, wherein the polyester resin composition includes either one or both of alkali metal atoms and alkaline earth metal atoms in an amount of 0.000005 to 0.05 parts by mass based on 100 parts by mass of the polyester resin A, and a content of linear oligomers of polybutylene terephthalate or the like is not more than 1000 mg/kg.