We investigate the quasiparticle interference (QPI) in Fe-based superconductors in both the s₊₊-wave and s_±-wave superconducting states on the basis of the five-orbital model. In the octet model for cuprate superconductors with d_x²−y²-wave state, the QPI signal due to the impurity scattering at q=k_i−k_j (E=|Δ(k_i)|, i=1−8) disappears when the gap functions at k_i and k_j have the same sign. However, we show that this extinction rule does not hold in Fe-based superconductors with fully gapped s-wave state. The reason is that the resonance condition E=|Δ(k_i)| is not satisfied under the experimental condition for Fe-based superconductors. We perform the detailed numerical study of the QPI signal using the T-matrix approximation, and show that the experimentally observed QPI peak around q₂=(π,0) can be explained on the basis of both the s₊₊-wave and s_±-wave states. Furthermore, we discuss the magnetic field dependence of the QPI by considering the Zeeman effect, and find that the field-induced suppression of the peak intensity around q₂ can also be explained in terms of both the s₊₊-wave and s_±-wave states.