A flange on a shaft of a fluid dynamic bearing unit is to be provided with a hole connecting an outer periphery of the flange and an outer periphery of the shaft. A radial groove is provided on a surface of two flange half pieces, and a vertical groove communicating with the radial groove is provided on an inner circumferential surface of the flange half pieces. Upon combining the two flange half pieces with the grooves facing each other and attaching them to the shaft, a path connecting an outer periphery of the flange and an outer periphery of the shaft is formed. The groove may be formed in a desired cross-sectional shape such as a semicircle, triangle or rectangle. The groove may be formed only on either of the flange half pieces, and the groove can be formed by a simple process such as pressing.