An apparatus for measuring vehicle speed is disclosed. The apparatus includes a pair of disk plates having a circular opening in a central part through which a final output shaft of a transmission passes by a plurality of long-shaft bolts with the plates being mounted to the final output shaft of the transmission by the plurality of long-shaft bolts. A plurality of reinforcement ribs are provided for coupling the pair of disk plates to each other with the ribs being arranged to be in an equal interval along the direction of the circumference of the disk plates in order to maintain a constant interval between the disk plates. A bracket is mounted around the disk plates with the bracket having a groove for receiving a circumferential section of the disk plates. A photosensor is mounted on the side of the bracket in order to sense a passing of the reinforcement ribs during a revolution of the disk plates with the photo-sensor applying a pulse signal to a controller of a vehicle control system generated by sensing the passing of the reinforcement ribs.