[Problems] Thermoplastic resins have various problems such as enhancement in strength and improvement in toughness and heat resistance and copolymerization with monomers or oligomers and grafting have been carried out to solve the problems. Although graft polymerization with macromonomers has been carried out as a method for solving the problems, it is still expected to develop a modification technique for attaining better performance and resins produced by the technique.[Means for Solving Problems] A thermoplastic resin obtained by addition polymerization of an addition-polymerizable monomer, characterized by being modified by copolymerization with a vinyl polymer (I) which bears at least one group having a polymerizable carbon-carbon double bond at each of at least two molecular ends and which has a weight-average molecular weight (Mw)/number-average molecular weight (Mn) ratio of less than 1.8.