Abstract: Provided are a flame retardant composition for expandable styrene resin that can be used to produce a foamed molded article having excellent flame retardancy and excellent heat resistance, a flame-retardant expandable styrene-based resin composition, and an extrusion-foamed molded article of the styrene-based resin compostion. The flame retardant composition for expandable styrene resin of the present invention comprises at least tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) as a component (B1), fatty acid zinc as a component (C), and a fatty acid metal salt, excluding the component (C), as a component (D), the component (C) being contained in an amount of 0.1 to 15 parts by mass based on 100 parts by mass of the component (B1), and the component (D) being contained in an amount of 1 to 35 parts by mass based on 100 parts by mass of the component (B1).