Provided is an additive for imparting ultraviolet absorbency, or an additive for imparting a high refractive index, which has satisfactory compatibility with a resin serving as a matrix and can maintain high transparency even if added in high concentrations. Also provided is an additive with which the function of imparting both ultraviolet absorbency and a high refractive index can be realized by means of one kind of additive. This additive is represented by the following Formula (I): wherein at least one of R1a to R9a is a monovalent sulfur-containing group represented by the following Formula (i-1) or Formula (i-2): R10amSH  (i-1) R11anSR12a—SpR13a  (i-2) wherein R10a to R12a each represent a divalent hydrocarbon group or the like; and R13a represents a monovalent hydrocarbon group or the like.