PURPOSE: To eliminate the generation of flow mark and to reduce the development of birefringence by a method wherein liquid reactive material is poured in a mold, between the top force and the bottom force of which spacers shrinkable in response to the polymerization shrinkage are arranged, and released from the mold when semi- cured.

CONSTITUTION: An outer periphery spacer 3 and a center spacer 4, both of which are formed by cutting a silicone rubber sheet in the predetermined doughnut-shapes and do not hinder the polymerization, are arranged between a top force 1 and a bottom force 2. In the resultant mold P, liquid reactive material is poured. After that, the material is polymerized by heat or ultraviolet rays. Though the amount of cure shrinkage in the direction of the thickness during polymerization is large, no flow mark is generated, because the provision of spacers shrinkable in response to the cure shrinkage prevents the local separation from the inner surface of the mold and the shifting of uncured monomer to the shrinkage gap from occurring. Next, after being released from the mold P when liquid reactive material is semi-cured, a board for disc is fully cured by the energy of heat or of ultraviolet rays. Accordingly, the strain in a molded item such as disc board or the like is lowered and the item with small birefringence is obtained.