An object of the present invention is to prevent loss of oil film and improve lubrication performance of the bearing by eliminating angled portions at butting surfaces in a two-piece retainer. A two-piece retainer is made by assembling a pair of semi-annular retainer parts into an annular structure. As assembled, lubricant reservoir grooves are formed, each by two arc-shaped groove wall surfaces which are formed on both sides of the butting surface, and by a groove bottom which is formed at a region including the butting surface.