The structure of adsorbed bromine on the Ag(100) electrode has been studied with the in-situ XAFS (X-ray absorption fine structure) method. In the near edge XAFS (NEXAFS), the 1s-4p transition was clearly observed, which indicates that the electron transfer occurs from bromide anion to the silver substrate and the bond is partly covalent. The Br-Ag distance was determined to be 2.82 +/- 0.05 Angstrom, which is shorter than that of the bulk AgBr. The adsorption site was revealed to be a fourfold hollow site. These results suggest that the bromide ionicity is reduced in the adsorbate phase on the electrode.