We discuss direct CP violation in three-body decays of B meson such as B + /-->K + /-π + π - , which involves various intermediate resonance states, such as B + /-->K * i π + /- and B + /-->ρK + /-, where K * i represents the πK resonance. Due to the large final state interaction phases of the resonances, the CP asymmetry can be as large as the 25% level near the kinematical region where the K * i and ρ resonances overlap. By examining a Dalitz plot of this mode and combining a measurement of the branching ratio for B + /-->ρ + /-K, it is possible to extract the weak phase, φ 3 =arg(-V u d V u b * /(V c d V c b * )), of the Kobayashi-Maskawa matrix.