PURPOSE: To obtain an optical transmission body of high performance by supplying monomers that form a high refractive index polymer into a rotating pipelike polymn. vessel while changing their mixing ratios gradually.

CONSTITUTION: A polymn. initiator is added to two kinds of monomers expressed by the formulaI(X denotes H or CH3, and R denotes C1WC16 hydrocarbon groups or fluorohydrocarbon groups) and these are put into supply vessels 1, 2, and are mixed through feed ports at the ratios obtd. by controlling the supply rates of two kinds of the monomers with gear pumps 3, 4. While the mixing ratios are changed in such a way as to increase the supply rate of the low refractive index monomer in the initial stage and to increase that of the high refractive index monomer gradually, these are injected into a pipelike polymn, vessel 10 rotating in a heating bath 9 along a driving shaft 8 which is revolved by a motor 6 via a driving belt 7.