The three-dimensional structure of the magnetic field in the source region of CMEs is the key to understand how the stored magnetic energy eventually causes an eruption. Particularly, a CME accompanied by a filament eruption on 2000 February 26-27 is a good event to study the three-dimensional magnetic field structure. This event was very well observed with SOHO/EIT and LASCO, Yohkoh, and the Nobeyama Radioheliograph. Based on the preliminary analysis, we found the following clues to study the 3-D magnetic field structure which causes the CME.


 - The helical structure of the filament before the eruption is kept during the eruption up to about ten solar radii.


- The coronal loop structure shows that this event is an eruption of a part of the quadrapolar magnetic field structure consisting of two active regions.


 In the meeting, we will discuss the presumed three-dimensional magnetic field of the CME source region.