To provide a video signal transmitting device for transmitting an SMPTE(The Society of Motion Picture and Television Engineers) standard serial digital video signal under reliable clock transfer.

This video signal transmitting device is provided with a means for latching a serial digital signal(SDI signal) by a clock and outputting the serial digital signal, a first light source for outputting an optical signal with the latched SDI signal, a means for performing two-frequency dividing of the clock and outputting a clock auxiliary signal, a second light source which outputs an optical signal with the clock auxiliary signal and whose wavelength is different from that of the first light source, and a means for multiplexing the output light of the first light source and the output light of the second light source. Thus the device performs transmission by a wavelength multiplex system by means of the same optical fibers.