PURPOSE: To produce a curing resin which has a low refractive index, is tough and is transparent by constituting the resin of a fluorine-contg. compd. having a specific high viscosity, specific fluorine-contg. (meth)acrylate and multifunctional monomer having ≥2 (meth)acryloyl groups in the molecule.

CONSTITUTION: This resin consists of the fluorine-contg. compd. A expressed by the formula I [Rf and R'f are a fluorinated aliphat. group of 3W20C, Z1 and Z2 are the formula II (R1 is H, alkyl group of 1W10C), Z3 is -(CH2)m- (m is 2W6 integer), R is H, methyl group, halogen atom, X1WX3 are the formula III (R2 is H, alkyl group of 1W36 or alkenyl group) A is the formula IV (R3 is H, methyl, etc.)], the fluorine-contg. (meth)acrylate B expressed by the formula V [R"f is a fluorinated aliphat. group of 3W20C, X is -SO2N(R1)- or -CON(R1)- (R1 is the same as mentioned above), (a) is 0 or 1, l is 1W6 integer, R is the same as mentioned above] and the multifunctional monomer C contg. ≥2 (meth) acryloyl group in the molecule.