In a thrust bearing supporting a load in a thrust direction in a rotary portion, a size of a curved surface in the forward side of a lubricating groove with respect to a relative rotating direction of an opposing sliding member is set to be larger than a size of a curved surface in the rearward side of the lubricating groove with respect to the relative rotating direction, and a depth of the lubricating groove is set to be deeper than a starting point in the side of a groove bottom of the curved surface formed in the groove shoulder in the forward side of the lubricating groove with respect to the rotating direction, so that a lubricating effect and a cooling effect are increased.