  We present our study of the dependence of the heavy-to-light semileptonic B
decay form factors on the heavy-light meson mass $M_{PS}$. Simulations are made
over a range of the heavy quark mass covering both the charm and bottom quarks
using the $O(a)$-improved clover action at $\beta=5.9$ on a $16^3\times 40$ and
$24^3\times 64$ lattice. We find that a weak dependence of form factors on
$M_{PS}$ observed in previous studies in the region of charm quark persists up
to the region of$b$ quark. The soft pion relation $f^0(q^2_{max})=f_B/f_\pi$ is
examined and found to be largely violated.
