An earthquake of M7.4 occurred off Tokaido region of southeast off the Kii Peninsula, Japan, on September 5, 2004, accompanied with a foreshock of M7.1 which proceeded about 5 hours and was located off the Kii Peninsula about 40km west from the main shock. Aftershock distribution were divided into 4 groups; the area of the M7.1 foreshock along the axis of the Nankai trough (group I), the area of the M7.4 main shock along the axis of the trough (group II), the area perpendicular to the trough axis containing the main shock (group III), and the area apart from the main shock in NE direction (group IV). The CMT solutions of groups I and II are thrust fault type that has a pressure axis in almost N-S direction. The focal mechanisms of group III are strike-slip fault type that has a nodal plane with the strike in NW-SE direction. The strike direction of the NW-SE direction is consistent with the aftershock distribution. The focal mechanisms of group IV are strike-slip fault type that has a nodal plane with similar strike but with an opposite slip direction to the group III. Micro-earthquakes with magnitude 3 began to occur in the main shock area, corresponding to occurrence of the foreshock of M7.1. The focal mechanisms of these earthquakes show the type of the group II. Aftershock activity of the main shock in both areas of group II and group III began almost at the same time. The aftershock activity shows ordinary decay with time, however, the number of earthquakes in the NW area of the group III decreased rapidly with time. In addition, slightly low frequency earthquakes occurred in the NW part of group III. Thus the group III is suggested to have different characters from groups I and II.