The present invention provides a plasticizer for a polylactic acid resin that has high compatibility with the polylactic acid resin, does not decrease the forming/processing temperature of the polylactic acid resin, and is less likely to bleed from a formed product over time. The present invention also provides a polylactic acid resin composition that has high plasticity and formability and can be formed and processed even at high temperatures. The present invention also provides a polylactic acid resin formed product that is formed of the resin composition, has high plasticity, and causes no bleedout of a plasticizer. A plasticizer for a polylactic acid resin according to the present invention contains a (meth)acrylic resin. The (meth)acrylic resin is a copolymer of monomer components containing 30 to 70 parts by weight of methyl methacrylate and 30 to 70 parts by weight of an alkyl acrylate having an alkyl group having 1 to 8 carbon atoms (the monomer components are 100 parts by weight in total), has a weight-average molecular weight in the range of 10,000 to 1,000,000, and has a molecular weight distribution in the range of 3 to 10.
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