  Using multi-wavelength data of Hinode, a rapid rotation of a sunspot in
active region NOAA 10930 is studied in detail. We found the extra-ordinary
counterclockwise rotation of the sunspot with positive polarity before an X3.4
flare. From a series of vector magnetograms, it is found that the magnetic
force lines highly sheared along the neutral line accompanying the sunspot
rotation. Furthermore, it is also found that the sheared loops and an inverse
S-shaped magnetic loop in the corona formed gradually after the sunspot
rotation. The X3.4 flare can be reasonably regarded as a result of this
movement. The detailed analysis provides an evidence that sunspot rotation
leads to magnetic field lines twisting in the photosphere, the twist is then
transported into the corona, and finally flares are triggered.
