In a laboratory simulation experiment of the earth's magnetosphere, an evidence of the existence of an earthward electric field is shown in the equatorial current sheet. The earthward electric field may be generated as a result of Hall electric field generation in the current sheet. A simple theoretical model for the existence of an earthward electric field is presented. The ions in the current sheet are accelerated by this earthward electric field, which then penetrate into the near earth dipole magnetic field. At the end of the current sheet near the earth, these ions are accumulated due to the difference of the inertia between ions and electrons. The polarization of charges reverses the electric field from earthward to tailward at this region. The experimental results have shown two directional electric fields along x-axis in the current sheet. The earthward direction of the electric field is due to the dawn-dusk current sheet carried by electrons. These experimental results prove the theoretical prediction. A discussion of the application of this result to the real magnetotail physics is also presented. ¿ American Geophysical Union 1993