A vehicle driving assistance device , comprising: an external information acquisition unit configured to acquire external information on a host vehicle; a three-dimensional object recognition unit configured to recognize three-dimensional objects ahead of the host vehicle, from the external information acquired by the external information acquisition unit ; a host vehicle travel route estimation unit configured to estimate a host vehicle travel route and to identify a preceding vehicle traveling ahead on the host vehicle travel route by selecting and specifying a three-dimensional object from registered three-dimensional objects to be tracked which have been registered by a three-dimensional object tracking processing unit ; and a leaving determination processing unit configured to determine leaving of the preceding vehicle from the host vehicle travel route relative to a preceding vehicle position information (P) obtained by the host vehicle travel route estimation unit as the three-dimensional object to be tracked located on a most front side on the host vehicle travel route , wherein the preceding vehicle position information (P) includes a measurement range which is set at a horizontal center position of the host vehicle travel route within a distance range between the preceding vehicle and the host vehicle, characterised in that the vehicle driving assistance device is configured to determine that the preceding vehicle left the host vehicle travel route in a case when a calculated distance range associated with the preceding vehicle, and obtained by dividing the parallax into vertical strips, exceeds a threshold value in a traveling direction of the vehicle, said threshold being increased by adding a fixed amount to the distance between the preceding vehicle and the host vehicle. an external information acquisition unit configured to acquire external information on a host vehicle; a three-dimensional object recognition unit configured to recognize three-dimensional objects ahead of the host vehicle, from the external information acquired by the external information acquisition unit ; a host vehicle travel route estimation unit configured to estimate a host vehicle travel route and to identify a preceding vehicle traveling ahead on the host vehicle travel route by selecting and specifying a three-dimensional object from registered three-dimensional objects to be tracked which have been registered by a three-dimensional object tracking processing unit ; and a leaving determination processing unit configured to determine leaving of the preceding vehicle from the host vehicle travel route relative to a preceding vehicle position information (P) obtained by the host vehicle travel route estimation unit as the three-dimensional object to be tracked located on a most front side on the host vehicle travel route , wherein the preceding vehicle position information (P) includes a measurement range which is set at a horizontal center position of the host vehicle travel route within a distance range between the preceding vehicle and the host vehicle, characterised in that the vehicle driving assistance device is configured to determine that the preceding vehicle left the host vehicle travel route in a case when a calculated distance range associated with the preceding vehicle, and obtained by dividing the parallax into vertical strips, exceeds a threshold value in a traveling direction of the vehicle, said threshold being increased by adding a fixed amount to the distance between the preceding vehicle and the host vehicle. <EOS>