PURPOSE: To transmit many color signals via an optocal fiber without using a photoconductive material by converting a signal containing many color wavelengths into spot light to produce spectral diffraction in a prism and transmitting the spot light via the optical fiber.

CONSTITUTION: A light source containing many color wavelengths is first led to an optical fiber 21 via a lens 23 in the form of the coherent spot light and made incident as it is on an incident face X of a prism 20 to produce spectral diffraction. Each of these separated color wavelengths is led to each corresponding optical fiber of an optical fiber group 22 to be transmitted in the form of a signal of the coherent signal color light. Then these signals are synthesized into many color signals having high fidelity.