To optimize optical behavior of the entire fiber amplifier by making optical behavior changing according to the temperature of an optical component of an optical fiber amplifier to be opposite to the optical behavior of a doped amplification fiber.

This optical fiber amplifier 1 has a light input 3 and a light output 4. These input and output are respectively connected to an optical transmission section 5. The optical fiber amplifier includes a pumping light source 8 connected to an amplification fiber component 2 through a coupler 9. Meanwhile, the component 2 is connected to an optical component 6. A signal to be transmitted is supplied into the fiber amplifier through the input 3. Pumping light from the source 8 is also supplied to the propagation direction of the signal through the coupler 9. An optical signal is amplified in an amplification fiber 2. In such a case, optical behavior changing according to the temperature of the component 6 of the amplifier 1 is at least opposite to the optical behavior of the doped amplification fiber 2.