  We report a measurement of the branching fraction for the decay $B^+ \to
\rho^+\pi^0$ based on a 140 ${\rm fb}^{-1}$ data sample collected with the
Belle detector at the KEKB asymmetric $e^+e^-$ collider. We measure the
branching fraction ${\cal B}(B^+ \to \rho^+\pi^0)=(13.2\pm 2.3({\rm
stat.})^{+1.4}_{-1.9}({\rm sys.}))\times 10^{-6}$, and the CP-violating
asymmetry ${\cal A}_{CP}(B^\mp \to \rho^\mp\pi^0)=0.06\pm0.19({\rm
stat.})^{+0.04}_{-0.06}({\rm sys.})$.
