To obtain a molding resin composition which has a good balance between flame retardancy and tracking resistance and is suitable for use as a voltage-resistant part by compounding a thermoplastic polyester resin with a specific organobromine compound and an antimony compound.

The composition comprises a thermoplastic polyester resin, an organobromine compound having a bromine content of 60wt.% or higher and a benzene ring concentration of 20wt.% or lower, and an antimony compound. The organobromine compound usually serves as a flame retardant. The benzene ring concentration refers to the ratio of the weight of the carbon atoms constituting the benzene rings to that of the compound. If the flame retardant has a bromine content lower than 60wt.%, it should be added in a larger amount in order to obtain high flame retardancy and this makes it difficult to achieve high tracking resistance. If the benzene ring concentration exceeds 20%, tracking resistance decreases.