  CP violation from physics beyond the Standard Model is investigated in
$B_{l4}$ decays: $B\to D\pi l\bar{\nu}_l$. The semileptonic $B$-meson decay to
a $D$-meson with an emission of single pion is analyzed with heavy quark
effective theory and chiral perturbation theory. In the decay process, we
include various excited states as intermediate states decaying to the final
hadrons, $D+\pi$. The CP violation is implemented in a model independent way,
in which we extend leptonic current by including complex couplings of the
scalar sector and those of the vector sector in extensions of the Standard
Model. With these complex couplings, we calculate the CP-odd rate asymmetry and
the optimal asymmetry. We find that the optimal asymmetry is sizable and can be
detected at $1\sigma$ level with about $10^6$-$10^7$ $B$-meson pairs, for some
reference values of new physics effects.
