The strong CP problem can be solved by parity symmetry with extended gauge symmetry. We first review two classes of models: the ones with the minimal fermion content and the ones with the minimal Higgs content. We then focus on the latter class of models and discuss a dark matter model where the stability of dark matter accidentally arrises from the extended gauge symmetry. The enough stability of dark matter provides an upper bound on the parity symmetry breaking scale. We then discuss a neutrino mass model and show that in the minimal model the neutrino mass is generated by quantum corrections. New gauge-singlet fermions in the model may be discovered by near-future experiments.