An optical material having a high refractive index and a wide transmission wavelength range and being free from anisotropy. A cubic system crystal material composed of alphabetaO3 is employed, where alpha is at least one of K, Ba, Sr and Ca, and beta is at least one of Ta and Ti. Preferably, a cubic system single crystal material composed of KTa1-xNbxO3, where the composition x satisfies a relation 0<=x<=0.35, is employed, and refractive index is enhanced furthermore while keeping the phase transition temperature lower than the room temperature. |