A driving assistance device sets, in front of an own vehicle, an actuation region that is a region sandwiched by boundary lines, positioned at left and right, respectively. In a case where a target existing around the own vehicle has entered the actuation region, the device performs driving assistance for avoiding collision with the target or mitigating collision damage. The device, when setting the actuation region, in a case where the own vehicle is in a turning state, changes a lateral position of a boundary line in an outside in a turning direction of the own vehicle, of the left and right boundary lines of the actuation region, to a position closer to the own vehicle according to turning information. For a boundary line in an inside in a turning direction of the own vehicle, the device does not change a lateral position according to the turning information.