The wavelength multiplex transmission device of the present invention includes a block band unit (block dispersion compensating unit etc.) for subjecting a plurality of signal lights of different wavelengths to dispersion compensation on a band basis and outputting the compensated signal lights, a CW light output unit (CW light source unit etc.) for outputting a CW light which supplements power of the signal light, a band multiplexing unit for multiplexing all the signal lights output from the block band unit together with the CW light output from the CW light output unit, and a total band optical amplifier for amplifying all the signal lights multiplexed by the band multiplexing unit in the lump and transmitting the amplified signal lights to a transmission path.