Provided is technology that causes polybutylene terephthalate resin to react with a reactive compound and reduces the thermal decomposition of the polybutylene terephthalate resin, when performing reactive processing method using the polybutylene terephthalate resin. During production of polybutylene terephthalate resin pellets, the polybutylene terephthalate resin (A) and a reactive compound (B) that reacts with the polybutylene terephthalate resin (A) are reacted such that the difference between the intrinsic viscosity of a polybutylene terephthalate resin composition configuring the polybutylene terephthalate resin pellets and the intrinsic viscosity of a polybutylene terephthalate resin composition configuring a polybutylene terephthalate resin molded article is no more than 0.05 dL/g, and the amount of carboxylic group ends in the resin included in the polybutylene terephthalate resin pellets is adjusted so as to be no more than 25 meq/kg.