To provide a structure capable of highly precisely regulating a positional relationship between an encoder 4c and a sensor unit 12 even if having a structure not to directly support the sensor unit 12, out of the encoder 4c and sensor unit 12 for measuring axial load, by an outer ring 1, or a stationary ring.

Nonmagnetic spacers 23a and 23b are impregnated and fixed to a tip end face and a side face of the sensor unit 12. The sensor unit 12 is brought into contact with the surface of the encoder 4c via both spacers 23a and 23b, so as to position the sensor unit 12 with respect to the encoder 4c and, in that state, the sensor unit 12 is supported and fixed to a knuckle 17a of a suspension device. Alternatively, a material used for both spacers 23a and 23b is a soft material such that portions coming into slide contact with the surface of the encoder 4c may be abraded and fallen therefrom after the use.