  Feasibility of a measurement of the partial decay width of the
intermediate-mass Higgs boson into two photons at a photon-photon collider is
studied by a simulation. The QCD radiative correction for quark pair background
processes is taken into account for the realistic background estimation. It is
found that the two-photon decay width can be measured with the statistical
error of 7.6 % with about one year of experiment. The impact of the measurement
of the two-photon decay width to look for the new physics beyond is
demonstrated.
