Resin composition for easily dyeable synthetic fibers, and synthetic fiber easily dyeable with acidic dye

A resin composition comprising:

• a polymer (A);
• and
• a polymer (B),
• wherein the polymer (A) is a modacrylic resin, and the modacrylic resin is a copolymer of acrylonitrile, one or more halogenated monomers selected from the group consisting of a vinyl halide and a vinylidene halide, and a macromonomer having, in a main chain, a polymer composed of a double bond-containing ethylenically unsaturated monomer,
• the polymer (B) is a polymer that is soluble in benzyl alcohol, and the polymer (B) is a polymer that comprises one or more monomer units selected from the group consisting of vinyl acetate, vinylpyrrolidone, acrylic acid esters, methacrylic acid esters, and styrene, and
• the resin composition comprises the polymer (A) in an amount of 70 parts by mass or more and 92.5 parts by mass or less, and the polymer (B) in an amount of 7.5 parts by mass or more and 30 parts by mass or less, where a total amount of the polymer (A) and the polymer (B) is 100 parts by mass.