  We present a model-independent study of the effects of a neutral Higgs boson
without definite CP-parity in the process $\gamma\gamma \to t\bar{t}$ around
the mass pole of the Higgs boson. Near the resonance pole, the interference
between the Higgs-exchange and the continuum amplitudes can be sizable if the
photon beams are polarized and helicities of the top and anti-top quarks are
measured. Study of these interference effects enables one to determine the CP
property of the Higgs boson completely. An example of the complete
determination is demonstrated in the context of the minimal supersymmetric
standard model.
