Spin-injection effect on magnetic state and transport properties of a magnetic junction is investigated. A three-layered magnetic junction is considered that consists of (i) a single-domain hard magnetic layer 1 with fixed orientation of the magnetic moment, (ii) a single-domain soft magnetic layer 2, and (iii) a thin dielectric layer in between with ballistic (specifically, tunnel) current transport through the latter. Spin-polarized electron injection from the layer 1 by an electric field applied to the junction creates a range of nonequilibrium spin polarization in the layer 2, the range width being of the order of the electron spin relaxation length. The energy of the s-d exchange interaction of injected free electrons and localized magnetic moments in that range is minimal in the case of parallel spin orientation. So, the exchange interaction tends to turn the localized magnetic moments in parallel to their orientation in the layer 1. The resulting orientation of the layer 2 magnetization is determined by minimum condition for the magnetic energy of the layer. The magnetic energy consists of the s-d exchange energy, the magnetic anisotropy energy and the Zeeman energy in the external magnetic field. The s-d exchange energy as a function of the angle between the injected electron spin direction and the layer 2 magnetization vector contains terms of zero, first and second powers in cosine of the angle. It means that the s-d exchange is reduced effectively to a renormalization of the magnetic field and the anisotropy constant. The renormalized values depend on the applied voltage. If the layer 2 magnetic moment is aligned initially antiparallel to the layer 1 magnetic moment by an external magnetic field then antiparallel to parallel switching is possible at some threshold voltage. It leads to stepwise decrease in the junction resistance and corresponding increase in the current through the junction. At reverse change of the applied voltage the inverse switching occurs at another (lower) voltage so that the current – voltage characteristic of the junction contains a hysteresis loop. Such behavior was observed in experiments repeatedly.