A polyester resin composition contains a polyester resin A containing 50 to 100 mass % of a polybutylene terephthalate resin and 0 to 50 mass % of a polyethylene terephthalate resin. The polyester resin composition further contains a predetermined amount of a metal organic acid salt B, which is either or both of an alkali metal organic acid salt and an alkaline earth metal organic acid salt; a predetermined amount of a styrenic resin C; and a predetermined amount of an inorganic filler D. The amount of linear oligomers of polybutylene terephthalate or the amount of the linear oligomers of polybutylene terephthalate and linear oligomers of polyethylene terephthalate is less than or equal to 1000 mg/kg. Inorganic filler D has an average particle size of 0.05 to 3 μm.