To provide a bearing device reducing a potential difference caused between a rotor portion and a stator portion during the drive of an underwater rotary machine, and having a permanent and effective function to prevent electrolytic corrosion without increasing a coefficient of friction.

A grease reservoir 9c is provided in the axial end of a rotating shaft 1 around which a bearing inner ring 5 is stationarily fitted, and a conductor 10c extending from either a bearing bracket 6 in which a bearing outer ring 7 is stationarily fitted or a bearing cover 10b covering the center portion of the bearing bracket 6 is inserted into the grease reservoir 9c. The conductive grease 11 is retained in the grease reservoir 9c to electrically connect the bearing bracket 6 to the rotating shaft 1.