An automatic arc-length method for geometrically non-linear finite element analysis of the structure subjected to the conservative and non-conservative forces is presented. This scheme can find the post buckling equilibrium path such as snap-through and turning-back which can not be traced by the load incremental scheme or the displacement incremental scheme. In the case of the analysis of the structure subjected to the non-conservative forces, the total tangent stiffness matrix becomes unsymmetric and when calculating the incremental load and unbalanced load vector components, the direction change of the non-conservative forces is considered. Several example problems to demonstrate the feasibility of the present arc-length method are given and discussed.