The objective of this study is to evaluate the effect of stress relief groove on fretting fatigue strength. Fretting fatigue tests and finite element analyses were done. The shape of groove was controlled by groove radius R and tangential angle θ. The depth of groove was specified by R and θ. Fretting fatigue strength was increased with an increase of θ and then it turned into a decrease. The decrease was caused by the transition of failure mode from fretting fatigue at the contact part to plain fatigue at the groove root. The transition was caused by an increase of stress concentration at the groove root with an increase of the groove depth. Therefore, the maximum improvement of fatigue strength was achieved by the largest θ limited by fatigue strength of the groove root. In the analysis, the groove generates high compressive stress field at the contact edge, where small cracks never propagate. Therefore, assumptions to relieve the contact pressure concentration at the contact edge were taken into the analysis model. The values of stress intensity factor ranges for small cracks introduced near the contact edge were almost the same between grooved and non-groove specimens.