A driving assistance device (100; 200) configured to execute deceleration assistance for a driver's vehicle when the driver's vehicle turns right or left at an intersection, the driving assistance device (100; 200) comprising: an adjacent vehicle recognizer configured to recognize, based on a detection result from an external sensor of the driver's vehicle, an adjacent vehicle (N1; N3; N4; N5) traveling in an adjacent lane that is adjacent to a traveling lane of the driver's vehicle; an adjacent vehicle travel determiner (13; 21) configured to determine whether the adjacent vehicle (N1; N3; N4; N5) turns in the same direction of the driver's vehicle at the intersection based on adjacent vehicle information acquired by vehicle-to-vehicle communication with the adjacent vehicle (N1; N3; N4; N5) or the detection result from the external sensor when the adjacent vehicle (N1; N3; N4; N5) is recognized by the adjacent vehicle recognizer and the driver's vehicle turns right or left at the intersection; a deceleration assistance executer (16; 27) configured to execute the deceleration assistance to cause a vehicle-to-vehicle distance between the driver's vehicle and the adjacent vehicle (N1; N3; N4; N5) in a traveling direction of the driver's vehicle to reach a distance equal to or larger than a preset target driver's vehicle-to-adjacent vehicle distance when the adjacent vehicle travel determiner (13; 21) determines that the adjacent vehicle (N1; N3; N4; N5) turns in the same direction of the driver's vehicle; a preceding vehicle recognizer configured to recognize, based on the detection result from the external sensor, a preceding vehicle traveling ahead of the driver's vehicle; and a large-sized vehicle determiner configured to determine whether the preceding vehicle is a large-sized vehicle based on preceding vehicle information acquired by vehicle-to-vehicle communication with the preceding vehicle or the detection result from the external sensor when the preceding vehicle is recognized by the preceding vehicle recognizer, wherein the deceleration assistance executer (16; 27) is configured to execute the deceleration assistance to increase a vehicle-to-vehicle distance between the driver's vehicle and the preceding vehicle when the large-sized vehicle determiner determines that the preceding vehicle is the large-sized vehicle as compared with a case where the large-sized vehicle determiner does not determine that the preceding vehicle is the large-sized vehicle. an adjacent vehicle recognizer configured to recognize, based on a detection result from an external sensor of the driver's vehicle, an adjacent vehicle (N1; N3; N4; N5) traveling in an adjacent lane that is adjacent to a traveling lane of the driver's vehicle; an adjacent vehicle travel determiner (13; 21) configured to determine whether the adjacent vehicle (N1; N3; N4; N5) turns in the same direction of the driver's vehicle at the intersection based on adjacent vehicle information acquired by vehicle-to-vehicle communication with the adjacent vehicle (N1; N3; N4; N5) or the detection result from the external sensor when the adjacent vehicle (N1; N3; N4; N5) is recognized by the adjacent vehicle recognizer and the driver's vehicle turns right or left at the intersection; a deceleration assistance executer (16; 27) configured to execute the deceleration assistance to cause a vehicle-to-vehicle distance between the driver's vehicle and the adjacent vehicle (N1; N3; N4; N5) in a traveling direction of the driver's vehicle to reach a distance equal to or larger than a preset target driver's vehicle-to-adjacent vehicle distance when the adjacent vehicle travel determiner (13; 21) determines that the adjacent vehicle (N1; N3; N4; N5) turns in the same direction of the driver's vehicle; a preceding vehicle recognizer configured to recognize, based on the detection result from the external sensor, a preceding vehicle traveling ahead of the driver's vehicle; and a large-sized vehicle determiner configured to determine whether the preceding vehicle is a large-sized vehicle based on preceding vehicle information acquired by vehicle-to-vehicle communication with the preceding vehicle or the detection result from the external sensor when the preceding vehicle is recognized by the preceding vehicle recognizer, wherein the deceleration assistance executer (16; 27) is configured to execute the deceleration assistance to increase a vehicle-to-vehicle distance between the driver's vehicle and the preceding vehicle when the large-sized vehicle determiner determines that the preceding vehicle is the large-sized vehicle as compared with a case where the large-sized vehicle determiner does not determine that the preceding vehicle is the large-sized vehicle.