An optical synthetic resin composed of: a synthetic resin; and fine particles dispersed in the synthetic resin at a ratio of 0.1 vol % or more to 50 vol % or less, each having a maximum length of 1 nm or more to 30 nm or less, in which part of surfaces of the fine particles are modified with functional groups which themselves repel each other, and a distance between two arbitrary adjacent fine particles among the fine particles is in a range of 0.1 nm or more to 500 nm or less. The two arbitrary adjacent fine particles attract each other with an intermolecular force, thereby making it possible to provide an optical composite deviating from an additivity range.