To provide a technology capable of enhancing the detection accuracy of a wheel speed detector and suppressing the cost.

The wheel speed detector 50 for a rear wheel is constituted of a pulse ring 52 attached to a rear wheel hub 18 and a pulse count sensor 60 attached to a swing arm 35 and the pulser ring is constituted of a disk 55 and pulser detection holes 57, etc., opened on the pitch circle drawn at a place near the center of specific distance from the outer edge of the disk 55. As a result of this, a pulse detection hole is opened close to the center side of the pulser ring outer edge, and thus a warp of the pulser ring at the edge can be suppressed.