  A consistent treatment of $B\rightarrow \pi l \nu$ decay is given on the
light-front. The $B$ to $\pi$ transition form factors are calculated in the
entire physical range of momentum transfer for the first time. The
valence-quark contribution is obtained using relativistic light-front wave
functions. Higher quark-antiquark Fock-state of the $B$-meson bound state is
represented effectively by the $|B^*\pi\rangle$ configuration, and its effect
is calculated in the chiral perturbation theory. Wave function renormalization
is taken into account consistently. The $|B^*\pi\rangle$ contribution dominates
near the zero-recoil point ($q^2\simeq 25$ GeV$^2$), and decreases rapidly as
the recoil momentum increases. We find that the calculated form factor
$f_+(q^2)$ follows approximately a dipole $q^2$-dependence in the entire range
of momentum transfer.
