Crack energy density in an arbitrary direction εφ is expected to describe fracture behaviors of a mixed-mode crack. It was shown previously that εφ can be evaluated by a path independent integral with practically sufficient accuracy. In this paper, as an another evaluation method of εφ, a method based on the relationship between εφ and load-displasement curves is discussed. The contents are as follows ; 1) A relationship between initial crack lengths, load-displacement curves and εφ which holds until cracks start to grow is derived by considering the strain energies of the specimens with different initial crack lengths. A method to evaluate εφ from load-displacement curves is proposed based on this relationship. 2) Based on the method, the evaluation of εφ is tried from load-displacement curves obtained by finite element analyses and also experiments for specimens under tension with a crack inclined to the loading axis, and it is shown that the method is practical for evaluating εφ through the comparisons with the theoretical values and the values evaluated by the path-independent integral.