In order to detect the amount of fatigue damage in SUS304 steel, we were investigating the relationship between fatigue damage and the perpendicular leakage magnetic flux density caused by martensitic structure induced by cyclic stress. Plane bending fatigue tests were carried out at the temperate of 0°C, 30°C and 65°C. The main results obtained were as follows : (1) The magnetic flux density of the center in the specimen clearly increase with the increase of the bending stress and number of cycles. However it is difficult to estimate the fatigue damage with using method when the temperature changed during the test, since the martensitic transformation also depends on the temperature. (2) When repeating the stress below a fatigue limit, the value of magnetic flux density will not increase from a certain value. This indicates that fatigue damage is not advancing. (3) The final value of saturated magnetic flux density and σa/σω correlated each other even when the temperature differs.
