Wavelength dispersion adjustment agent, resin composition, and method for adjusting wavelength dispersion of resin

In the present invention, an additive is configured from a compound having a 9,9-bisarylfluorene skeleton represented by formula (1). [In the formula: ring Z indicates an aromatic hydrocarbon ring; R1 and R2 indicate a substituent group; X indicates the group -[(OR3)n-Y] (in the formula: Y indicates a hydroxyl group, a mercapto group, a glycydyloxy group, or a (meth)acryloyloxy group; R3 indicates an alkylene group; and n indicates an integer that is at least 0) or an amino group; k indicates an integer from 0 to 4; m indicates an integer that is at least 0; and p indicates an integer that is at least 1.] The additive can reduce the wavelength dispersion of a resin or can impart (or express) inverse wavelength dispersion properties in the resin.