A pulley support double row ball bearing is disclosed, which improves the seal performance of the seal rings and is able to maintain sufficient durability even under severe conditions. The ball bearing includes inner sections of the seal rings which overlap the end surfaces in an axial direction of the inner ring such that the width of the overlap in the axial direction is 30% or more than the diameter of the balls. Moreover, tip edges of first and second protrusions are formed on the inside surface of the seal lips and come in sliding contact with end surfaces of the inner ring. Furthermore, third protrusions come close to and face the corner sections of the inner ring to form labyrinth seals in those areas.