Charmless 3-body decays of B mesons are studied using a simple model based on the framework of the factorization approach. We have identified a large source of the nonresonant signal in the matrix elements of scalar densities, e.g. 〈KK|s̄s|0〉. This explains the dominance of the nonresonant background in B → KKK decays, the sizable nonresonant fraction of order (35 ∼ 40)% in Kππ and K 0 ππ modes ...