© 2018 authors. Published by the American Physical Society. We search for CP violation in the charged charm meson decay D+→π+π0, based on a data sample corresponding to an integrated luminosity of 921 fb-1 collected by the Belle experiment at the KEKB e+e- asymmetric-energy collider. The measured CP-violating asymmetry is [+2.31±1.24(stat)±0.23(syst)]%, which is consistent with the standard model prediction and has a significantly improved precision compared to previous results.