A 1.3 .mu.m-band optical amplifier includes an optical amplifying fiber doped with Yb ion for emitting light in 1.02 .mu.m band by pumping of the 0.98 .mu.m band light and Pr ion for amplifying signal light by pumping of the 1.02 .mu.m band light. Both ends of the optical amplifying fiber are connected to optical fiber gratings for selectively reflecting 1.02 .mu.m band light via matching connecting members and tapered core optical fibers. The optical fiber gratings form a 1.02 .mu.m-band resonator. A Wavelength Division Multiplexing (WDM) optical coupler multiplexes the signal light and pumping light from an pumping laser and supplies the thus-multiplexed light to the optical fiber grating. The pumping laser comprises a laser device which causes laser oscillation at 0.98 .mu.m. A 1.5 .mu.m-band optical amplifier having a similar configuration is also disclosed.