The 0(+) states of He-8 are studied in a five-body He-4+n+n+n+n cluster model. Many-body resonances are treated on the correct boundary condition as Gamow states using the complex scaling method. The 0(2)(+) state of He-8 is predicted as a five-body resonance in the excitation energy of 6.3 MeV with a width of 3.2 MeV, which mainly has a (P3/2)(2)(P1/2)(2) configuration. In this state, number of the 0(+) neuron pair shows almost two, which is different from the ground state having a large amount of the 2(+) pair component. The monopole transition of 8He from the ground state into the five-body unbound states is also evaluated. It is found that the He-7 + n component mostly exhausts the strength, while the 0(2)(+) contribution is negligible. The final states are dominated by He-6+n+n, not He-4+n+n+n+n. The results indicate the sequential breakup process of He-8 -> He-7 + n -> He-6 + n + n by the monopole excitation. (C) 2010 Elsevier B.V. All rights reserved.