Disclosed are an apparatus for mass polymerization of a vinyl chloride resin which may suppress generation of abnormal products (fine-particle products, oversize-particle products, lumpy products due to coagulation, etc.) and a vinyl chloride resin, which causes formation of a poor sphere, and may enhance quality and processability of a vinyl chloride resin, by addressing the problem that an average distance between resin particles is decreased as polymerization proceeds, and thus, microparticles are generated due to excessive coagulation or friction between particles, and a method of mass-polymerizing the vinyl chloride resin. The method comprises additionally inputting a monomer to a reactor in which a monomer and an initiator are contained when a ratio of the monomer converted to a polymer is 30% to 70%.