A technique has been known which detects obstacles around the vehicle using an object sensor such as an ultrasonic sensor (sonar) or a laser radar provided in the vehicle. Patent Literature 1 discloses an obstacle detection device using an ultrasonic sensor. An object of the technique is to prevent the occurrence of an error due to the interference between noise and signals transmitted or received by the sensor. In the technique, a sensor which can change a transmission frequency is used and the transmission frequency and reception sensitivity of the sensor when noise is detected are different from those in a normal state. In this way, an operation error due to noise and a change in a detection area are prevented.