The authors have conducted in-phase and 90° out-of-phase push-pull and torsion fatigue tests on SUS304 stainless steel at 550°C and investigated its fracture mechanism and fatigue failure criterion. This paper assesses the results of the push-pull and torsion fatigue tests which have the shear strain to normal strain ratio of 1.5 with 30°, 45°, 60° phase difference at 550°C and discusses the transition condition of the fracture mode and the low cycle fatigue failure criterion for the biaxial fatigue data obtained in this study as well as for those in the previous study. From the strain analysis and the fracture surface observation in the in-phase and out-of-phase tests, the fracture mode transition condition which depends on both the values of Δεmax/Δγmax and Δεn/Δγmax was determined, and the biaxial fatigue fracture mode map for a SUS304 stainless steel at 550°C was drawn on the basis of these values. Equivalent strain energy, ΔE, was defined by iso-fatigue life evaluation from a plane with tensile strain energy, ΔEI on the y-axis and shear strain energy, ΔEII, on the x-axis. Fatigue failure life under out-of-phase straining conditions could be correlated well with equivalent strain energy.