An optical switch disposed in intermediate positions of optical paths to define a channel of a light signal constitutes a cell member in whose interior cells are formed and a waveguide member having fine slits; and a gas is filled in cells of which side walls are formed by piezoelectric/electrostrictive elements or antiferroelectric elements, a liquid is filled in the fine slits, and the cells and the fine slits are communicated to each other via a communicating hole; optical waveguides intersect at the fine slits, and the-cells are disposed at the crossing locations, and said side walls are expanded/constricted by applying an electric field to the piezoelectric/electrostrictive elements or antiferroelectric elements which form the side walls of the cells, and a part of the gas stored in each cell is ejected at a corresponding intersection area from said communicating hole into the corresponding fine slit.