To obtain a composition capable of retarding the depolymerization of a poly(methyl methacrylate) grafted on a main chain of a propylene polymer material and facilitating a melt processing thereof without increasing a content of a monomer or small by adding a specific hydroxyl amine compound thereto.

This composition includes (B) 0.025-0.5 pts.wt. compound of the formula T1T2NOH [T1 is a 1-36C alkyl, a 5-12C cycloalkyl, a 7-9C aralkyl, etc.; T2 is H or T1] added to and mixed with (A) 100 pts.wt. grafted copolymer obtained by grafting a poly(methyl methacrylate) or a copolymer of methyl methacrylate and other monomers on (A1) a propylene polymer material. The total amount of the grafted monomer is 20-120 pts.wt. based on 100 pts.wt. component A1, and the amount of a comonomer is ≤20mol% of the total amount of the monomer when the comonomer is used.