The method and apparatus can manufacture a plastic sheet of uniform thickness and reduced distortion, by use of metallic molds and in accordance with cast molding polymerization (casting) technique. The plastic sheet manufacturing apparatus for manufacturing a plastic sheet by injecting a raw material into a polymerization cell (101) and by polymerizing the injected raw material by heat, includes a pair of first and second molds (104A, 104B) for forming the polymerization cell (101); and first and second heat conductors (102, 103) attached to both outside surfaces of the first and second molds, respectively, so as to be opposed to each other and to sandwich the first and second molds therebetween. Here, in particular, each of the first and second heat conductors is formed with a fluid passage (210) therein to circulate a heated fluid whose temperature is controlled.