  By treating CP-violating interaction as a perturbative term, we solve the
Dirac equation in the background of electroweak bubble wall (the distorted wave
Born approximation). We obtain the transmission and reflection coefficients for
a chiral fermion incident from the symmetric-phase region and for the one from
the broken-phase region respectively. There hold the respective sets of
unitarity relations and also reciprocity relations among them. These relations
enable us to rigorously derive quantum-number flux through the bubble wall,
which is the first order quantity of the CP violation. The flux is found to be
negligible for a thick wall such that $m_0/a\gsim 2$, where $1/a$ is the wall
thickness and $m_0$ is the fermion mass.
