To provide a driver alert system capable of improving the safety. A bicycle includes a first transmission circuit transmitting a first ultrasonic wave, a first receiving circuit receiving a second ultrasonic wave, an arithmetic circuit detecting the presence or absence of an object from the second ultrasonic wave, and a second transmission circuit transmitting a third ultrasonic wave. A driver wears a second housing including a second receiving circuit receiving the third ultrasonic wave. The arithmetic circuit includes a first selection circuit selecting a potential based on the second ultrasonic wave at a different timing, a plurality of signal retention circuits retaining a potential based on the second ultrasonic wave, a second selection circuit selecting any one of the plurality of signal retention circuits, and a signal processing circuit to which a signal selected in and output from the second selection circuit is input. The second selection circuit selects the plurality of signal retention circuits at different timings to generate a signal obtained by delaying the second ultrasonic wave. The third ultrasonic wave generated on the basis of the signal is transmitted to the second housing.