There is provided a wide-band optical amplifier (10) that is capable of amplifying a wide-band signal. The wide-band optical amplifier (10) includes a first amplifier (NOPA1) that emits, based on a to-be-amplified light beam having a predetermined range of wavelengths and a first pump beam (L2) having a first wavelength, the to-be-amplified light beam having a first range of amplified wavelengths, where the first range is a part of the predetermined range, and a second amplifier (NOPA2) that emits, based on the to-be-amplified light beam having the first range of amplified wavelengths and a second pump beam (L3) having a second wavelength different from the first wavelength, the to-be-amplified light beam having a second range of amplified wavelengths, where the second range is different from the first range.