The effect of strain-induced martensite and introduced strain was examined in thermo-mechanical treatment for grain refinement on the SUS304 metastable-austenitic stainless steel. By combining the cold working with warm working, the following were independently estimated : Effect of the strain and effect of the martensite. In spite of whether it added to before and after anyway of the martensite generation, the strain has the equivalent effect for grain refinement. Resembled microstructure and mechanical property in high temperature was shown.