Processing assistant for expansion molding, vinyl chloride resin composition for expansion molding, and expansion molded body

Disclosed is a vinyl chloride resin expansion molded body having fine and uniform foam cells and excellent appearance.  Also disclosed are a processing assistant for expansion molding, which is useful for production of the vinyl chloride resin expansion molded body, and a vinyl chloride resin composition for expansion molding.  The processing assistant for expansion molding comprises a polymer (A) which is obtained by polymerizing a monomer component (a) containing not less than 65% by mass of isobutyl methacrylate, and the polymer (A) has a reduced viscosity (η sp /c) of not less than 4, when measured at 25˚C by dissolving 0.1 g of the polymer (A) into 100 ml of chloroform.