We investigate the electronic state and the superconductivity in the 5-orbital Hubbard model for iron pnictides by using the dynamical mean-field theory together with the linearized Eliashberg equation. The renormalization factor exhibits a significant orbital dependence resulting in the band-dependence of the mass enhancement. The critical interactions towards the magnetic, orbital and superconducting instabilities are calculated and found to be suppressed as compared to the corresponding RPA results due to the correlation effects. Remarkably, the s_<++>-pairing phase due to the orbital fluctuation is expanded as compared to the RPA result, while the s_±-pairing phase due to the magnetic fluctuation is largely reduced.