To prevent magnetic force from being disturbed in N-poles, S-poles, and a boundary part between them, in a ring-shaped magnet member formed with a magnetized surface where N-poles and S-poles are alternately magnetized in the circumferential direction of a magnet base material formed into a ring-like shape.

In this ring-shaped magnet member, the magnet base material 20 molded into a ring-like shape by injecting a magnet material into dies 11 and 12 from a pin gate 12a are planarly magnetized, and the magnetized surface 23 is formed by alternately magnetizing the N-poles and the S-poles in the circumferential direction of the magnet base material. In the ring-shaped magnet member, the magnetized surface is formed on the opposite surface side of pin gate parts 21 corresponding to the pin gate, and the pin gate parts and weld parts 22 of boundaries where magnet materials contact each other in molding are made absent at boundary positions between the N-poles and the S-poles.