To provide a fiber optics amplifier system having a highly simplified structure.

The fiber optics amplifier comprises a lasing fiber, a pumping light source for pumping the lasing fiber, and an optical coupler having coupling efficiency depending upon wavelengths. The optical coupler comprises a signalling optical fiber port for transmitting a signal to be amplified, a pumping light optical fiber port for transmitting pumping light, and a signal/pumping light combined use optical fiber port. The signal/pumping light combined use optical fiber port is optically coupled with one end of the lasing fiber to transmit the signal to be amplified between the optical coupler and the lasing fiber, while causing population inversion in a lasing substance by transmitting the pumping light to the lasing material in the lasing fiber. Hereby, the signal is amplified with induced radiation when the signal passes through the lasing fiber.