To avoid or suppress the deformation (projection or warping) of the portions corresponding to spoke portions in a periphery when a cast disk shape blank is forged.

The cast disk shape blank is set in a first die, and is pressed by moving a second die toward the first die, and is forged so as to reduce the thickness of the spoke portions. Long and narrow projecting stripes 41x elongating in the direction crossing the spoke portions are formed on the spoke forming surfaces in the second die 40. By the projecting stripes 41x, the plastic flow of the spoke portions of the cast disk shape blank in the radial direction in forging can be suppressed.