To provide an impact strength improving agent which is added a little to a resin to furnish it with improved impact resistance and better workability, and can provide a molded product with adequate discoloration resistance.

The impact strength improving agent is an acrylic elastomer graft copolymer having an acid group and obtained by graft copolymerizing (B) a vinyl monomer to (A) a polyalkyl(meth)acrylate composite elastomer, wherein the polyalkyl(meth)acrylate composite elastomer contains two or more acrylic elastomer components which have their different glass transition temperatures (Tg).