To provide a polylactic acid resin composition that has excellent strength, flame retardancy, and durability and especially has excellent flexural strength when molded into a thin molding.

The polylactic acid resin composition is a resin composition containing: 100 pts.mass of a polylactic acid resin (A); 35-135 pts.mass of a flame retardant (B) based on a metal salt of an organophosphinic acid; 85-230 pts.mass of glass fiber (C) with a flat cross section; 5-40 pts.mass of a carbodiimide compound (D) having an isocyanate group; and 0.05-30 pts.mass of a crystal nucleating agent (E), wherein the total mass of the components except (A) is 150-300 pts.mass.