Double row tapered roller bearing, bearing ring, and method for producing double row tapered roller bearing

A double row tapered roller bearing comprising:

• an outer ring serving as a bearing ring having an annular shape;
• an inner ring disposed on an inner circumferential side of the outer ring and serving as a bearing ring having an annular shape, the inner ring having an outer circumferential surface facing the outer ring and having two rows of grooves having a bottom surface serving as a raceway surface;
• and
• tapered rollers disposed in the grooves in contact with the raceway surface of the inner ring and being also in contact with the outer ring,
• at the outer circumferential surface of the inner ring, a region adjacent to the groove including a hardened region extending from an inner peripheral surface of the groove to the region adjacent to the groove, and an unhardened region located at a position farther from the groove than the hardened region and being smaller in hardness than the hardened region,
• the region adjacent to the groove being located outside of the groove, and forming a boundary between the hardened region and the unhardended region on the outer circumference surface.