Plastic constraint and local strain at the notch root for notched plates and bars were examined in the elastic-plastic and full plastic regions by FEM. By introducing the mean equivalent stress, σ(Mises), and the strain, ε, at the minimum cross section, and the equivalent stress concentration factors, Kt, the results obtained in this study are summarized as follows: (1) The plastic constraint factor k defined by σ/σn was nearly constant under the wide range of deformations, and independent of the material constants. (2) The general yield stress σGY was derived based on the idea that the mean equivalent strain in the elastic state is almost equal to that in the plastic state. (3) The relationship between σ and ε for σ≥σGY was approximately in accord with the constitutive equation of the materials and was ε=Bσm for σ≤σGY. (4) The equivalent strain, ε, at the notch root was simply estimated from ε=Kt ε.