  We propose a hybrid seesaw model based on $A_{4}$ flavor symmetry, which
generates a large hierarchical flavor structure. In our model, tree-level and
one-loop seesaw mechanisms predict different flavor structures in the neutrino
mass matrix, and generate a notable hierarchy among them. We find that such a
hierarchical structure gives a large effective neutrino mass which can be
accessible by next-generation neutrinoless double beta decay experiments.
Majorana phases can also be predictable. The $A_{4}$ flavor symmetry in the
model is spontaneously broken to the $Z_{2}$ symmetry, leading to a dark matter
candidate which is assumed to be a neutral scalar field. The favored mass
region of the dark matter is obtained by numerical computations of the relic
abundance and the cross section of the nucleon. We also investigate the
predictions of the several hierarchical flavor structures based on $A_{4}$
symmetry for the effective neutrino mass and the Majorana phases, and find the
characteristic features depending on the hierarchical structures.
