A rolling bearing is constructed so that, even though adapted for seals, strength of the bearing rings and reduction of the front width will not occur. Also dimensions equivalent to a non-sealed type bearing can be achieved. Rolling elements are disposed between an inner ring and an outer ring with seals provided. One seal is fitted in a pressed state on a peripheral surface portion of a cylindrical surface forming a counterbore of the outer ring. By pressing, the seal is mounted without forming a slot. The other seal is fitted in a slot. The inner ring and the outer ring, or rolling elements of a bearing comprising the outer ring, inner ring, rolling elements and a retainer are subjected to carbonitriding and a grease using a urea compound as a thickening agent is sealed in the bearing.