By running pseudo-dynamic tests on an full-scale flexible-stiff mixed frame extracted from a five-story actual buiding applied the "first-story energy-concentrated steel structure with flexible-stiff mixed frames" to, following matters were confirmed : The applied building was ductile and stable during a limit earthquake. Most of input energy due to a severe earthquake can be absorbed as cumulative inelastic strain energy by stiff members in the first story and flexible members remain elastic. Performance and results indicate that this structural system is safe under severe earthquakes.