Stress state in a region involving a bearing surface is an important subject to be investigated for higher reliability of bolted joints. This report shows equivalent stress distributions obtained from FEM analyses and particularly discusses stress states in both sides of bearing surfaces in cases of using several kinds of bolt It is found that a hexagon head bolt with flange with a proper concavity angle can bring improvements of unevenness of the stress distribution and strength reliability in the region. This effect is owing to uniforming of pressure distribution on a bearing surface caused by the concavity angle. However, application of this effect requires proper selection of this angle.