Resin composition for improving adhesive strength, resin molded article, bonded article, and agent for improving adhesive strength

Disclosed is a technique for improving the adhesiveness of a resin molded article comprising a polyalkylene terephthalate resin to a silicone-based adhesive. A mixture of (A) a modified polyalkylene terephthalate resin obtained by copolymerizing an aromatic dicarboxylic acid excluding terephthalic acid and/or an esterified product thereof as a modifying component and (B) an unmodified polyalkylene terephthalate resin, in which the content of the modifying component is adjusted in a specific range, is used. It is preferred that the modified polyalkylene terephthalate resin is a modified polybutylene terephthalate resin, and the aromatic dicarboxylic acid and/or an esterified product thereof is isophthalic acid and/or an esterified product thereof.