An inner cladding exposure section 14 is formed by removing a part of an outer cladding 4 of an optical amplification medium fiber 10 which has a porous layer 3 between the inner cladding 2 and the outer cladding 4 in a longitudinal direction. An end surface 23 of an optical fiber 20 for the excited light incidence is cemented on an outer periphery of the exposed inner cladding 2. The excited light 24 is incident into the optical amplification medium fiber 10 from the optical fiber 20 for the excited light incidence. By doing this, it is possible to provide a method for exciting a light in an optical amplification medium fiber which can realize a superior amplitude while emitting the excited light so as to be incident into the optical amplification medium fiber highly efficiently.