A residue of a Regge pole of a partial wave amplitude is shown to be factorized. The high energy behavior of total cross section is shown to be written as though a Fermion pair has 4 spin states. If only the Pomeranchuk term dominates at high energies, the following relations among total cross sections are obtained: Several conditions to be satisfied by spectral functions of Lehmann's representation (in order that the scattering amplitudes have Regge behaviors) are given.