Vehicle speed calculator

A vehicle speed calculator 200 provided on a motorcycle has vehicle speed calculation means 218 to calculate a vehicle speed from a travelled distance per unit time of a feature point in an image of a road surface captured by a camera 100. The vehicle speed calculator 200 includes reference distance mark irradiation means 108 and image reference distance detection means 216. The reference distance mark irradiation means 108 irradiates a reference distance mark onto the road surface, and the reference distance mark has a reference distance in a longitudinal direction of the motorcycle 10. The image reference distance detection means 216 detects an image reference distance, the longitudinal length of the reference distance mark in the captured image. The vehicle speed calculation means 218 calculates the vehicle speed from the travelled distance using the image reference distance and the reference distance. The vehicle speed calculator offers improved calculation accuracy of vehicle speed even in the event of a change in vehicle height.