The electronic structure of {Fe_3-xV_xM} (M=Al, Ga) alloys was investigated by ab initio method. Magnetic and non-magnetic band structure of {Fe_3-xV_xM} was calculated for concentrations x=0.0--1.0. Calculations have shown that the transition from magnetic to non-magnetic state is accompanied by the qualitative changes in the band structure in the vicinity of the Fermi level ({\varepsilon _F}). For concentrations 0.5\le x\le 1 the Density Of States (DOS) at {\varepsilon _F} in both magnetic states display a sharp peak composed solely of the 3d states of impurity Fe-AS atom ( Fe atom at nominally V atom position of {Fe₂VAl} Heusler compound). In the magnetic state only majority-spin states enter the DOS near {\varepsilon _F}. The quasi-gap around the {\varepsilon _F} found in {Fe₂VM} is filled up by 3d  states of Fe-AS which produce the sharp structures at {\varepsilon _F}. Transition to the non-magnetic state results in the narrowing and strengthening of the peak of Fe-AS 3d-states DOS at {\varepsilon _F} and the opening of the well-defined gap just above the Fermi level. The changes of the DOS around {\varepsilon _F} connected with the variation of Fe-AS concentration and magnetic transition explain the peculiar behavior of the electrical resistivity observed experimentally.

PACS numbers: 72.10.--d, 72.15.--v, 71.20.Eh, 71.20.--b