  A distinct peak is observed in the pi^+/- psi' invariant mass distribution
near 4.43 GeV in B->K pi^+/- psi' decays. A fit using a Breit Wigner resonance
shape yields a peak mass and width of 4433+-4(stat)+-2(syst) MeV and Gamma =
45^+18_-13(stat) ^+30_-13 MeV. The product branching fraction is determined to
be Bf(B-->KZ(4430))xBf(Z(4430)-->pi^+psi') =
(4.1+-1.0(stat)+-1.4(syst))x10^{-5), where Z(4430) is used to denote the
observed structure. The statistical significance of the observed peak is
6.5sigma. These results are obtained from a 605 fb-1 data sample that contains
657 million BBbar pairs collected near the Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric energy e+e- collider.

High Energy Physics - Experiment