In a bearing device, a double row rolling bearing for supporting a pinion gear-side portion of a pinion shaft on a case (annular wall) is formed by a tandem-type double row angular contact ball bearing. A first row of balls having a larger pitch circle diameter are disposed between inner and outer rings of the double row angular contact ball bearing at a region near to the pinion gear, and a second row of balls having a smaller pitch circle diameter are disposed between the inner and outer rings at a region remote from the pinion gear. A bearing internal space is divided into a first bearing internal space containing the first ball row and open toward the pinion gear and a second bearing internal space containing the second ball row and sealed by partition walls formed respectively by bearing seals, lubricating grease being sealed in the second bearing internal space.