A light diffusing agent which contains a copolymer that contains: a (meth)acrylate structural unit represented by general formula; and a polyvalent vinyl structural unit that is copolymerizable with the structural unit, wherein the copolymer is a polymer microparticle having an average particle diameter of 0.1 to 100 μm, wherein the average particle diameter is calculated based on the particle size distribution as measured using a laser diffraction/scattering type particle size distribution measuring device, and wherein one (meth)acrylate compound of structural unit is solely used, wherein: X represents a divalent group selected from the group consisting of a single bond, -C(R 2)(R 3)-, -C(=O)-, -O-, -OC(=O)-, -OC(=O)O-, -S-, -SO-, -SO 2 - and any combination thereof, wherein R 2 and R 3 each independently represent a hydrogen atom, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a phenyl group or a phenylphenyl group; or R 2 and R 3 may be bonded to each other so as to form a cyclic alkyl group having 3 to 10 carbon atoms together with a carbon atom to which they are attached; Y represents a branched or unbranched alkylene group having 2 to 6 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms or an arylene group having 6 to 10 carbon atoms; R 1 represents a hydrogen atom or a methyl group; R 4 and R 5 each independently represent a linear alkyl group having 1 to 10 carbon atoms, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a halogen atom, a phenyl group or a phenylphenyl group; m represents an integer of 0 to 10; n represents an integer of 1 or 2; p represents an integer of 0 to 4; and q represents an integer of 0 to 5. a (meth)acrylate structural unit represented by general formula; and a polyvalent vinyl structural unit that is copolymerizable with the structural unit, wherein the copolymer is a polymer microparticle having an average particle diameter of 0.1 to 100 μm, wherein the average particle diameter is calculated based on the particle size distribution as measured using a laser diffraction/scattering type particle size distribution measuring device, and wherein one (meth)acrylate compound of structural unit is solely used, wherein: X represents a divalent group selected from the group consisting of a single bond, -C(R 2)(R 3)-, -C(=O)-, -O-, -OC(=O)-, -OC(=O)O-, -S-, -SO-, -SO 2 - and any combination thereof, wherein R 2 and R 3 each independently represent a hydrogen atom, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a phenyl group or a phenylphenyl group; or R 2 and R 3 may be bonded to each other so as to form a cyclic alkyl group having 3 to 10 carbon atoms together with a carbon atom to which they are attached; Y represents a branched or unbranched alkylene group having 2 to 6 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms or an arylene group having 6 to 10 carbon atoms; R 1 represents a hydrogen atom or a methyl group; R 4 and R 5 each independently represent a linear alkyl group having 1 to 10 carbon atoms, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a halogen atom, a phenyl group or a phenylphenyl group; m represents an integer of 0 to 10; n represents an integer of 1 or 2; p represents an integer of 0 to 4; and q represents an integer of 0 to 5. X represents a divalent group selected from the group consisting of a single bond, -C(R 2)(R 3)-, -C(=O)-, -O-, -OC(=O)-, -OC(=O)O-, -S-, -SO-, -SO 2 - and any combination thereof, wherein R 2 and R 3 each independently represent a hydrogen atom, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a phenyl group or a phenylphenyl group; or R 2 and R 3 may be bonded to each other so as to form a cyclic alkyl group having 3 to 10 carbon atoms together with a carbon atom to which they are attached; Y represents a branched or unbranched alkylene group having 2 to 6 carbon atoms, a cycloalkylene group having 6 to 10 carbon atoms or an arylene group having 6 to 10 carbon atoms; R 1 represents a hydrogen atom or a methyl group; R 4 and R 5 each independently represent a linear alkyl group having 1 to 10 carbon atoms, a branched alkyl group having 3 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, a linear alkoxy group having 1 to 10 carbon atoms, a branched alkoxy group having 3 to 10 carbon atoms, a cyclic alkoxy group having 3 to 10 carbon atoms, a halogen atom, a phenyl group or a phenylphenyl group; m represents an integer of 0 to 10; n represents an integer of 1 or 2; p represents an integer of 0 to 4; and q represents an integer of 0 to 5.