To provide a color developing device which can transit between a color developing state and a non-color developing state and which can maintain the color developing state even when the device is subjected to mechanical vibration.

The color developing device is equipped with a pair of transparent substrates 11, 12 having transparent electrodes 13, 14 disposed facing each other with a specified with a mixture filling the space between the substrates and consisting of a plurality of fine particles 16 having a smaller size than the specified gap and of an insulating fluid 15 having transparency for visible rays, and with a voltage applying means 17 to apply a voltage between the electrodes. When a voltage is applied on the pair of electrodes by the voltage applying means 17, such a structure that a plurality of the aforementioned fine particles are dispersed in the planes parallel to the aforementioned electrodes is formed, and colors are developed by introducing light into the mixture having the aforementioned structure.