A half thrust bearing for a crankshaft of an internal combustion engine is formed of a back metal layer and a bearing alloy layer to have a slide surface and two thrust reliefs. Each thrust relieve includes a first region, where the back metal layer is exposed, on a circumferential end surface side, and a second region, where the bearing alloy layer is exposed, on the slide surface side while the slide surface includes two third regions adjacent to the second region, and a fourth region between the two third regions. A circumferential end region consists of the first, second and third regions. In the second region and the third regions, the bearing alloy layer includes a uniform thickness portion at a radial center, and a decreased thickness portion adjacent to an inner-diameter-side end surface.