Disclosed are a belt type continuous plate manufacturing apparatus including two endless belts 11, 11′ with their facing belt surfaces running toward the same direction at the same speed, and a gasket 7 sandwiched by belt surfaces at their both side edge portions, in which a polymerizable raw material is fed into a space surrounded by the facing belt surfaces and the gasket from its one end, and solidified together with running of the belts in a heating zone, and a plate polymer is taken out from the other end, wherein a plurality of upper and lower roll pairs 4, 4′ each composed of an upper roll 4 and a lower roll 4′ and having axes orthogonally grossing the belt running direction are placed along the belt running direction as a mechanism of holding the belt surfaces of the endless belts 1, 1′ in the heating zone, and the outer diameter D of the roll body portion of the upper and lower roll pair is in the range of 100 mm to 500 mm; and a method of producing a plate polymer using this apparatus.