A formulation is presented to evaluate the critical length of an elastic long column that buckles due to its own-weight. The column is modeled as a serial assembly of rigid links and virtual springs that stand for the flexural rigidity of the column. The critical length is searched by the dynamic criterion as the one that makes the lowest natural frequency equal to zero, which is derived by the condition that the sum of the kinetic energy, strain energy and gravitational energy of the column vibration is kept constant. The numerical examples of an aluminum column demonstrates the validity of the present formulation.