PURPOSE: To provide an electric capillary optical switch which ensures a high speed operation in spite of miniaturization by providing the switch by a bypassing passage connected to both ends of a slit.

CONSTITUTION: Electrodes 1 are respectively arranged in the positions in contact with both ends of the slits 3. The respective electrodes 1 are connected to a power source by wirings. Mercury 2 is, therefore, eventually moved by electric capillarity in the slit 3 when a voltage is impressed between both electrodes 1. A bypassing groove 4 is formed at a glass plate which is a cap. Then, an electrolyte existing in front of the mercury 2 moves to a positive pole side through the bypassing groove 4 and moves backward of the mercury 2 at the time the mercury 2 is moved to a negative pole side by the electric capillarity in the slit 3 when the voltage is impressed between both electrodes 1. The bypassing groove 4 exists on both sides of the slit 3 at this time and, therefore, the electrolyte is eventually divided and moved in two directions and the resistance by viscosity is lowered. As a result, the movement of the mercury 2 is speeded up.