This study addresses the characteristics of the nightside magnetospheric current system using the analogy of an electric circuit. The modeled circuit consists of the generator (V: solar wind), inductor (L: tail lobes), capacitor (C: plasma sheet convection), and resistor (R: particle energization). The electric circuit has three time constants:Here τ CR is of the order of the ion gyroperiod in the plasma sheet, τ LC is a global timescale (2πτ LC is several tens of minutes), and τ L/R is even longer (several hours). Despite uncertainty in the estimate of each circuit element, τ CR ≪ τ LC ≪ τ L/R holds generally for the magnetosphere, which characterizes the electric circuit as overdamped. The following implications are obtained: (1) During the substorm growth phase the cross-tail current increases continuously even if interplanetary magnetic field (IMF) B Z does not change after southward turning; (2) the magnetotail current weakens following northward turnings if the change of IMF B Z is comparable to the preceding southward IMF B Z ; otherwise it may strengthen continuously if more gradually; (3) during the early main phase of magnetospheric storms the enhancement of the lobe magnetic energy is far more prominent than the enhancements of the kinematic and kinetic energies of the plasma sheet plasma; (4) The efficiency of the solar wind-magnetosphere coupling changes on a timescale of several hours (τ L/R ) through the change of the tail flaring, and so does the cross polar-cap potential; and (5) the magnetospheric current system does not resonate to an oscillatory external driver, and therefore, the periodicity of some magnetotail phenomena reflects that of their triggers.