An autonomous driving device including: vehicle side surroundings information detecting sensors; a left-right pair of extensions provided to a towing device, the extensions extending further to a vehicle width direction outside than a vehicle width direction outside end portion of the towed vehicle; a left-right pair of device side surroundings information detecting sensors, the device side surroundings information detecting sensors being respectively provided to the left-right pair of extensions and detecting surroundings information; and a control device controlling travelling of the autonomous vehicle based on detection results of the vehicle side surroundings information detecting sensors, and, in cases in which the device side surroundings information detecting sensors are electrically connected to the control device, controlling travelling of the autonomous vehicle based on the surroundings information detected by the device side surroundings information detecting sensors in addition to surroundings information detected by the vehicle side surroundings information detecting sensors.