A light modulator having a simple structure and a high operating speed. A light modulating device (1) has a magnetization setting layer (11) made of a magneto-optical material and including magnetization setting elements the directions of magnetization of which are independently set and each of which rotates the direction of polarization of incident light according to the direction of magnetization by the magneto-optical effect, thin-film coils (12) so provided as to correspond to the respective magnetization setting elements of the magnetization setting layer (11) and adapted to generate a magnetic field so as to independently set the direction of magnetization of each magnetization setting element, and a reflective layer (13) for reflecting light provided between the magnetization setting layer (11) and the thin-film coils (12). A drive section (2) changes the magnetization of the magnetization setting layer (11) into either the state in which the direction of the magnetization of all the magnetization setting elements is up or the state in which the direction is down. The lights emerging from the light modulating device (1) in the two states are separated according to the different directions of polarization by an analyzer (5).