An optical amplifier device comprising an input/output section that inputs incident light and outputs emission light; a polarized light splitting section that causes a polarized light component of the incident light input from the input/output section to branch, and outputs first polarization mode light having a first polarization and second polarization mode light having a second polarization different from the first polarization; a polarization converting section that receives the first polarization mode light, converts the first polarization to the second polarization, and outputs first polarization converted light; and an optical amplifying section that amplifies the first polarization converted light input to one end of a waveguide, outputs the resulting amplified first polarization converted light from another end of the waveguide, amplifies the second polarization mode light input to the other end of the waveguide, and outputs the resulting amplified second polarization mode light from the one end of the waveguide.