A Raman amplifying device includes a plurality of Raman amplifiers having a gain wavelength characteristic with a gain peak at which an amplification gain becomes the largest, including a first Raman amplifier having a gain wavelength characteristic with a plurality of gain peaks including a first gain peak and a second gain peak adjacent to the first gain peak; a second Raman amplifier having a gain wavelength characteristic with at least one gain peak including a third gain peak between the first gain peak and the second gain peak; and a third Raman amplifier having a gain wavelength characteristic with a fourth gain peak between the first gain peak and the third gain peak, the fourth gain peak forming an arithmetic sequence between the first gain peak and the third gain peak.