To hold a pulsar ring (1) of a magnetic rotary encoder well concentrically by a pressure inserting jig (4) when the pulsar ring is installed on a rotary body (3), the pulsar ring (1) comprises a metallic annular holder (10) and a pulsar main body (20) of a magnetic rubber material, the holder (10) comprises a disk portion (11) where the pulsar body (20) is bonded, a mounting tube portion (12) having a diameter smaller than the outer diameter of the disk portion (11) and being fixed to the rotary body (3), a fold-back portion (15) folded inward, and an intermediate portion (13) extending therefrom toward the mounting tube portion (12) so as to be separated from the disk portion (11), and the outer circumference of the fold-back portion (15) or a guide portion (22) mounted thereon is fitted to a circumferential wall portion (42) of the jig (4).