To provide a groove working device for a fluid bearing capable of efficiently and accurately working a dynamic pressure generating groove.

A cutting tool 4 is moved forward and backward, while rotating a spindle 2 supporting a thrust plate 1, to form the outside cylindrical surface 1a of the thrust plate 1 with several grooves at the same time. The cutting tool 4 is formed with several blade parts 8 projecting in the inside diameter direction from a part 7, in which the thrust plate 1 can be loosely inserted. A bore diameter circle connecting blade tips of the several blades 8 is arranged to have a diameter smaller than the outside diameter of the thrust plate 1.