1. A stable equilibrium point calculation apparatus of a power system, comprising: means for applying a pseudo-transient simulation method to a nonlinear differential algebraic equation of the power system including a mechanical system differential equation of a generator of the power system, in which a mechanical system damping factor of the generator in the power system is set to be greater, by a predetermined degree, than an actual mechanical system damping factor of the generator, thereby finding a norm of a mechanical system equation of the nonlinear differential algebraic equation of the power system including the mechanical system differential equation of the generator in which the mechanical system damping factor is set, wherein contingencies, on which an influence of virtual power system disturbances is reflected, is reflected as parameters of variables in the nonlinear differential algebraic equation of the power system; means for determining whether the found norm meets a predetermined condition; means for setting, when it is determined that the norm meets the predetermined condition, variable values of the nonlinear differential algebraic equation including the mechanical system differential equation of the generator at a time, when the value that is determined to meet the predetermined condition is found, as initial values of the variables of the nonlinear differential algebraic equation of the power system; and means for determining a stable equilibrium point (SEP) by applying a Newton method to the nonlinear differential algebraic equation of the power system, in which the initial values are set.