A laboratory simulation experiment was performed to observe the dynamical behavior of the earth’s magnetosphere, based upon the earthward electric field measurement in the magnetotail. The simulation was examined to satisfy the MHD scaling laws. The earthward electric field, E x , is the signature of the current density based on j × B force in the tail, described by Podgorny (1978). The effect of the solar wind dynamic pressure to the earthward electric field, E x , was investigated. The solar wind density was changed while the other parameters were kept almost constant. It is found that the E x is modulated by the change in the solar wind dynamic pressure. The result also shows that the current continued to flow in the near earth region even after the solar wind had stopped. This result shows a similar resemblance to that of the particle confinement in the radiation belt of the real magnetosphere.