The device of this invention has a holder (12, 28) for holding the work (9, 27), work shafts (25, 26) on each of which the holder is mounted, and each of which feeds in the work in the axial direction, and grinding tools (15, 16) each arranged at a specified slope angle for grinding the aforementioned work (9, 27) to the prescribed spherical shape, the aforementioned work shafts (25, 26) and grinding tools (15, 16) being adapted for rough grinding and for precision grinding, respectively, and it is equipped with a transferring device (11, 13, 32, 33) for bringing the holder (12, 28) holding the aforementioned work (9, 27) to the work shaft (25) for rough grinding and to the work shaft (26) for precision grinding, further, the work shaft (25) for rough grinding being provided with a mechanism for forced cutting-in against the grinding tool (15), and the work shaft (26) for precision grinding with a mechanism for constant pressure cutting-in, whereby well finished surface may be realized at high efficiency and after-processings are spared. Accordingly, this invention is quite advantageous in maintenance and control of precision and cost reduction.