  We have studied a quinary Fe-based superconductor Sr$_2$VFeAsO$_3$ by the
measurements of x-ray diffraction, x-ray absorption, M\"{o}ssbauer spectrum,
resistivity, magnetization and specific heat. This apparently undoped
oxyarsenide is shown to be self doped via electron transfer from the V$^{3+}$
ions. We observed successive magnetic transitions within the VO$_2$ layers: an
antiferromagnetic transition at 150 K followed by a weak ferromagnetic
transition at 55 K. The spin orderings within the VO$_2$ planes are discussed
based on mixed valence of V$^{3+}$ and V$^{4+}$.
