To provide an optical fiber coupler for preventing an excitation light source from being damaged even if a signal light is leaked, and to provide an optical fiber amplifier using the same.

The optical fiber coupler 100 includes a first optical fiber 10 having a core 11 and a clad 13 covering the core 11, a second optical fiber 20 having a core 21, and a fusion extension 110 formed by fusion of the clad 13 of the first optical fiber 10 and the core 21 of the second optical fiber 20 by arranging the longitudinal direction of the first optical fiber 10 in the same direction of the longitudinal direction of the second optical fiber 20, wherein the refractive index of the clad 13 in the first optical fiber 10 is higher than that of the core 21 of the second optical fiber 20.