DRIVING ASSISTANCE DEVICE, VEHICLE, AND DRIVING ASSISTANCE METHOD

An acquisition unit acquires data regarding a travel trajectory of another vehicle from the other vehicle. A specifying unit specifies an intersection position between the travel trajectory of the other vehicle and a travel trajectory of a self-vehicle. A setting unit setts a region based on the intersection position and the travel trajectory of the other vehicle as a monitoring region when performing driving assistance. A determination unit determines whether or not to update the monitoring region based on a result of comparison between first data that is the data used to set the monitoring region and second data that is the data acquired from the other vehicle traveling in the monitoring region. The setting unit updates the monitoring region based on the second data in a case where the determination unit determines to update the monitoring region.