  In the case of two-generation Majorana neutrinos, we derive the oscillation
probabilities of $\nu \leftrightarrow \nu$, $\nu^c \leftrightarrow \nu^c$ and
$\nu \leftrightarrow \nu^c$ in a unified framework by using a relativistic
equation. We show that the Majorana phase occurs not from the violation of the
lepton number but the change of chirality. We also check the conservation of
the unitarity. Furthermore, we find that the oscillation probabilities of $\nu
\leftrightarrow \nu^c$ obtained in this paper is largely different from the
previous results in the point that there are no zero-distance effect and no
direct CP violation.
