A thrust bearing including a back metal layer and a sliding layer joined to a front face of the back metal layer. The thrust bearing having a thickness. The back metal layer includes an intermediate sub-layer and a buffer sub-layer disposed on a back face of the back metal layer. The sliding layer is joined to the intermediate sub-layer. Both of the sub-layers include iron or an iron alloy, and the buffer sub-layer has a thickness of 2 to 20% relative to the thickness of the thrust bearing, and a porosity ratio of 10 to 50%.