[Problem] In an optical amplifier, the excitation light level of an excited laser diode decreases, or, when the output of an excitation light is stopped, a backup excited laser diode is operated, and therefore the current consumption increases. [Solution] This optical amplifier is provided with multiple excitation laser diodes, a first current control element, a second current control element, and control means. The excitation laser diodes oscillate excitation light, the excitation light being inputted to an optical fiber amplifier. The first current control element controls a current flowing in the excitation laser diodes. The second current control element controls a current flowing in at least one of the excitation laser diodes. The control means controls the first current control element and the second current control element.