Kimura et al. [2, 3] has proposed the concept to realize beam yielding mechanism of a steel moment-resisting frame by applying a mid-story pin column base system. Controlling moment distribution, the system reliably prevents yielding of the first story columns. As design procedure to predict their elasto-plastic behavior, modified D-value method has been proposed. Previous papers  examined flexural strength of columns to keep them in elastic when frames were modeled as those having perfect elasto-plastic beams. In reality, however, bending moment keeps increasing due to strain hardening after beams yield. In this paper, the authors develop the modified D-value method to consider strain hardening effect. Using a proposed method, required flexural strength of columns is clarified to avoid them from yielding up to when the frame forms beam yielding mechanism. The results of the modified D-value method sufficiently agree with those of static analysis of low-to-mid-rise steel moment resisting frame. It is clarified that the story drift is reduced for larger strain hardening gradient, and that the maximum bending moment of the column does not change significantly, compared with those of perfect elasto-plastic frame.