An optical modulation method and apparatus uses superconductive oxide material for the optical modulation element. The current, magnetic field, temperature or pressure applied to the superconductive oxide material is varied so as to induce a superconduction-normalconduction transition, and the resulting variation in optical characteristics such as the reflectivity, transmissivity or refractive index of the superconductive oxide material modulate the input light. The method and apparatus are fast in operation and simple in structure. The method and apparatus also detect the variation in the current, magnetic field, temperature or pressure as a change in the reflectivity, transmissivity or refractive index of the superconductive oxide material on the basis of a superconduction-normalconduction transition.