Saddle-straddling type motor vehicle

A crank shaft is provided in a casing to be rotatable relative to the casing. A fan is provided to be integrally rotated with the crank shaft. A rotation angle sensor is arranged outside of the plate of the fan at one end of the crank shaft in the axial direction of the crank shaft on the rotational center axis of the fan. A detector and a portion to be detected of the rotation angle sensor are opposite to each other on the rotational center axis of the fan. One of the detector and the portion to be detected is provided to be integrally rotated with the crank shaft, and the other is provided not to be rotated relative to the casing.