of the wave combiner 50 consequently the signal light inputted to the doped fiber 46 is amplified by the same and then outputted from the same by way of the output port 48 in this manner with the optical amplification apparatus for an optical communication system according to the third embodiment of the present invention stabilized excitation light can be supplied to the doped fiber 46 by means of the excitation light source 49 the polarization holding fiber 51 and the depolarization section 52 and consequently there is an advantage in that otherwise possible deterioration of the signal to noise ratio of signal light can be suppressed it is to be noted that while the depolarization section 52 in the present embodiment is constituted from a splitter a birefringent optical material as delay time difference providing means and a wave combiner the construction of the depolarization section 52 is not limited to the specific one and the depolarization section 52 may otherwise be constituted only from a birefringent optical material this similarly applies to the following modifications to the present embodiment fig2 shows a first modification to the optical amplification apparatus for an optical communication system of the third embodiment of the present invention referring to fig2.