In machining a pocket (1) installing therein a rolling element, tools (7, 8) are prepared whose milling parts (5, 8a) have contours which coincide with the sectional configuration of the pocket resulting when the pocket has been machined along a retainer radial direction (Z), and the milling parts (5, 8a) of the tools (7, 8) are inserted into a prepared hole for the pocket which is provided in advance and are then translated in a retainer revolving direction (Y) and axial direction (X), respectively, for forming the pocket. Accordingly, it is possible to provide a retainer for rolling bearings that has high accuracy in machining pockets and which is suitable for an integral one-piece retainer.