  We present a multi-wavelength observation of a solar flare occurring on 2006
December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory, to study
the electron acceleration site and mechanism. The Solar Optical Telescope (SOT)
on board Hinode observed elongated flare ribbons, and RHESSI observed
double-footpoint hard X-ray (HXR) sources appearing in part of the ribbons. A
photospheric vector magnetogram obtained from SOT reveals that the HXR sources
are located at the region where horizontal magnetic fields change the
direction. The region is interpreted as the footpoint of magnetic separatrix.
Microwave images taken with the Nobeyama Radioheliograph show a loop structure
connecting the HXR sources. The brighter parts of the microwave intensity are
located between the top and footpoints of the loop. We consider these
observations as an evidence of the electron acceleration near the magnetic
separatrix and injection parallel to the field line.
