This paper deals with the effect of $N_2$ and $H_2$gas mixture ratio and ion-nitriding time in the corrosion fatigue fracture behavior of ion-nitrided SCM4 steel with notch subject to rotary bending stress. The specimens were treated rapid water cooling after ion-nitriding at $500^{circ}C$ Torr for 1 hour and 3 hours in gas mixtures of 80% $N_2$and 50% $N_2$. The fatigue limit and the fracture strength of corrosion fatigue depended on $N_2$gas quantity and ion-nitriding time. The ion-nitrided specimens showed about 88 .approx. 158% increase in the fracture strength of corrosion fatigue in $10^6$ cycles than non-nitrided specimens. The corrosion failure is due to corrosion pitting of the surface, and the propargation of cracks started at the surface into the core.