To provide an environment-conscious thermoplastic resin composition which has excellent mechanical strength, moldability and heat resistance, and is improved in flexibility.

The crystalline polylactic acid resin composition is a resin composition containing a polylactic acid resin (A) and a crystal nucleating agent (B) and is characterized in that: a mass ratio (A/B) of the polylactic resin (A) to the crystal nucleating agent (B) ranges from 90/10 to 99.9/0.1; the polylactic acid resin (A) is fused and kneaded with a (meth)acrylate compound (C) and a peroxide (D); and the crystal nucleating agent (B) comprises potassium dimethyl sulfoisophthalate and/or sodium dimethyl sulfoisophthalate.