Abstract: The present invention provides a diacetylene derivative represented by the following formula (A) which exhibits liquid crystallinity by itself and has a large refractive index anisotropy or does not exhibit liquid crystallinity by itself but exhibits a large refractive index anisotropy when added to a liquid crystalline compound: R1-Sp1-(Ar1)p-(Ar3)q-(Phe)r-C?C—C?C-(Phe)r-(Ar4)q-(Ar2)p-Sp2-R2??(A) (wherein R1 and R2 are a hydrogen, halogen, cyano, isothiocyanate, alkyl, alkenyl, alkynyl or reactive group, SP1 and SP2 are each a spacer group, Ar1 and Ar2 are each a non-substituted or substituted aromatic carbocyclic or heterocyclic group, Ar3 and Ar4 are each a non-substituted or substituted heterocyclic group, Phe is a non-substituted or substituted 1,4-phenylene group, and p, q and r are each 0 or 1.