Since magnetism in Fe-based superconductors (SCs) show many similarities to that in Cr, investigation of the overall spin dynamics of antiferromagnetic (AF) metal will give indispensable information about the relationship between AF spin fluctuations and high-Tc superconductivity. However, it is very far from complete understanding at present, because of experimental difficulties arising from the large energy scale of spin excitations in Cr. Here, we propose an INS experiment on MAPS using an alternate AF metal of Mn2.8Fe0.2Si, which is a similar system to Cr with a small energy scale. The aim is to explore sub-eV-order region at where neither Cr nor high-Tc SCs are investigated in each reduced energy scale. We will gain an insight into not only the hierarchical structure of spin excitations in itinerant-electron magnets but also the novel magnetic dispersive relation in high-Tc SCs.