The invention provides a thrust bearing, including a pair of half thrust bearings. Each half thrust bearing includes a bearing alloy layer and a resin slide layer, or a back metal layer, a bearing alloy layer and a resin slide layer. The resin slide layer constitutes a slide surface receiving an axial force of a crankshaft. Each half thrust bearing include thrust reliefs formed adjacent to both circumferential end portions of the sliding surface so that a wall thickness is thinner toward the circumferential end surface. A thrust relief length at an inner end portion of the thrust relief positioned on a rear side of one of the half thrust bearings in a rotational direction is larger than a thrust relief length at an inner end portion of the thrust relief positioned on a front side of the other of the half thrust bearing in the rotational direction.