  We investigate the relation between the rank I separable potential for the
covariant Bethe-Salpeter equation and the one-boson-exchange potential. After
several trials of the parameter choices, it turns out that it is not always
possible to reproduce the phase-shifts calculated from a single term of the
one-boson-exchange potential especially of the $\sigma$-exchange term,
separately by the rank I separable potential. Instead, it is shown that the
separable potential is useful to parameterize the total nucleon-nucleon
interaction.
