A roller bearing utilizing a roller retainer, which has an excellent assemblability in the sense that the assembly line can be automated and which eliminates various problems inherent in the full complement roller bearing The roller bearing includes an outer race having a raceway, a plurality of rollers held in rolling contact with the raceway, and a ring-shaped roller retainer having a plurality of pockets, each rollingly receiving the respective roller, spacedly defined therein in a direction circumferentially thereof to form a ladder-like structure. The roller retainer has a plurality of slits that are spacedly defined in a direction circumferential thereof so as to extend from one axial end or the other axial end of the roller retainer to a position adjacent the other axial end or one axial end.