From a linear 2-D eigenmode analysis, we found that the Hall current effect on collisional tearing mode instability becomes important for the thin magnetic reversal layer whose width is comparable to the ion inertia length; Hall currents produce a three dimensional field structure and increase the reconnection (growth) rate. Since the magnetic reversal layer widths both in the magnetopause and in the magnetotail are reported to become as thin as the ion inertial length (several hundred km) when the reconnection process is supposed to occur, the Hall current effect would have an observational significance. The Hall current effect may explain the appearance of the dawn-dusk component of the magnetic field in the magnetotail reconnection region.