To make it possible to inexpensively produce a sensor ring by pressing and to improve the detection accuracy of a detecting speed of the rotating speed by bending a plate material from the position of a groove of an annular ring with the groove faced on the inner side, thereby forming the sensor ring.

The sensor ring 1 is mounted coaxially with a hub of the axle of an automobile. The sensor ring is provided with a cylindrical part 6 to be press fitted to the fitting surface of the hub. Plural projecting parts 7 are formed by half shearing at an equal pitch over the entire circumference of sensing parts 8. Valley parts 9 are formed between the projecting parts 7. Rugged parts 11 are formed on the surfaces of the sensing parts 8 by both parts 7, 9. Proximity sensors 4 are installed to face the sensing parts 8. The formation thereof is executed by providing the annular plate material with the annular groove extending in the circumferential direction and bending the plate material from the position of the groove with the groove faced on the inner side. A line 14 is formed by bending the groove. The sensor ring 1 is formed with the projecting parts 7 and the valley parts 9 over the entire length in the diametral direction of the sensing parts 8.