To provide an ultra-precision polishing tool capable of machining the surface of a workpiece with high accuracy and efficiency and having high machining adaptability to free curved surfaces.

In an ultra-precision polishing tool for machining a surface to be machined by supplying machining fluid 4 in which abrasive grains 3 are dispersed in liquid and imparting relative movement between the tool and a workpiece, a fiber assembly consisting of element wires 2 of single fibers or threads formed by binding the element wires 2 is attached to a tool shaft and forces are applied from the element wires of the fiber assembly to free abrasive grains 3 in the machining fluid to give the free abrasive grains 3a machining force for the surface to be machined of the workpiece.