PURPOSE: To obtain an optical amplifier which eliminates the shape distortion of a signal wave due to the waveform dispersion of an optical fiber.

CONSTITUTION: An optical amplifier is composed of a wavelength multiplexer 12 whose signal optical terminal is connected to an input/output port 112 at an optical circulator 11 which is provided with an input port 111 for signal light, with the input/output port 112 and with an output port 113, an exciting light source 13 which is connected to the exciting light terminal of the wavelength multiplexer and which radiates exciting light, an optical amplification fiber 14, which is connected to the multiplexing terminal of the signal light and the exciting light which advances via the wavelength multiplexer, and a light reflection mirror 16, which is connected to the other terminal of the optical fiber for optical amplification. A chirp grating fiber 15 for dispersion compensation is connected across the optical amplification fiber and the mirror.