A light control apparatus includes a part for splitting an input light entering the light control apparatus through an optical fiber, a photoelectric conversion part for converting a monitor light into an electrical signal, and a third part for controlling the opening and closing of an optical transmission path for a signal light based on the electrical signal. The light power of an output light is controlled by the opening and closing amount of the optical transmission path which is controlled depending on the amount of the electrical signal output in accordance with the level of the monitor light. A semiconductor photovoltaic device capable of performing photoelectric conversion without using an external power source is used as the photoelectric conversion part. An optical shutter using a micromachine, or an optical device such as absorption-type modulator or refractive index-type modulator is used as the third part.