When a vehicle speed sensor is provided as a separate unit, the vehicle sensor should be removed when a vehicle wheel is changed. A brake caliper is fitted to an upper stay and a lower stay formed at a lower part of the front fork supporting the front wheel. The sensor stay is fitted to the inside of the lower stay in the vicinity of the brake caliper. A sensor cover is fastened integrally in an overlapping manner to the outside of the sensor stay. A projection formed on the sensor cover overlaps with a fitting bolt of the brake caliper. Thus, it is not possible to remove the brake caliper without first removing the sensor cover. Further, a vehicle speed sensor is sandwiched by the sensor stay and the lower end of the sensor cover and the three members are fastened together.