A fixing material includes a silane compound polymer as the main component, the silane compound polymer being produced by condensing a silane compound mixture that includes at least one silane compound (1) shown by the following formula (1): R1Si(OR2)p(X1)3-p (wherein R1 represents a group including an ester structure or a cyanoalkyl group, R2 represents an alkyl group having 1 to 6 carbon atoms or the like, X1 represents a halogen atom, and p is an integer from 0 to 3), and at least one silane compound (2) shown by the following formula (2): Si(OR3)q(X2)4-q (wherein R3 represents an alkyl group having 1 to 6 carbon atoms, X2 represents a halogen atom, and q is an integer from 0 to 4). A sealed optical device includes an optical device that is sealed with a cured product of the fixing material. The fixing material produces a cured product that exhibits high hardness, excellent transparency and heat resistance, and rarely undergoes coloration even when subjected to high-energy light or heat for a long time.