The asymmetric bias voltage dependence of the tunneling magnetoresistance (TMR) effect in Mn₈₀Ir₂₀/Ni₈₀Fe₂₀/Co₉₀Fe₁₀/SrTiO₃/La_0.7Sr_0.3MnO₃ (LSMO) junctions was investigated. The bias voltage dependence of the TMR effect depended on a chemical composition of SrTiO₃ (STO) barrier. In our previous report, the origin of the asymmetric bias voltage dependence of the TMR effect in such junctions was accounted for by the density of states of CoFe. However, it is necessary to consider the influences of the electronic structure in STO/LSMO, CoFe/STO interfaces, and oxygen deficiency in the STO barrier.