  We present our study on $B \to \pi l \nu$ semileptonic decay form factors
with NRQCD action for heavy quark from a quenched lattice QCD simulation at
$\beta$=5.9 on a $16^3\times 48$ lattice. We obtain form factors defined in the
context of heavy quark effective theory by Burdman et al. and find that their
$1/m_B$ correction is small. The limit of physical heavy and light quark masses
can be performed without introducing any model function, and we obtain a
prediction for the differential decay rate $d\Gamma/dq^2$. We also discuss the
soft pion limit of the form factors.
