Magnetic properties of Fe$_{50.1}$Mn$_{22.7}$Ga$_{27.2}$ alloy in connection with its atomic structure are investigated in temperature range of 4—850 K by using neutron diffraction (ND) and magnetometry. As revealed, the annealed (at 1020 K during 96 hours) and quenched (in ice water) alloy contains ordered phases of superstructural L1$_{2}$ and L2$_{1}$ types. The Fe$_{50.1}$Mn$_{22.7}$Ga$_{27.2}$ alloy exhibits complicated temperature dependence of magnetic properties determined by the ferromagnetic (FM)-to-paramagnetic transformation (under heating) in L2$_{1}$ phase and transformation from the antiferromagnetic (AFM) state to the FM one in L1$_{2}$ phase. As revealed with ND data, the AFM order in L1$_{2}$ phase is not strongly antiparallel. Absence of significant exchange anisotropy in the alloy can be explained by the random orientation of magnetic moments of the FM-phase grains, which are adjacent to the AFM-phase regions.