Vehicle driving assist system

In a vehicle driving assist system, an external environment recognition unit (5) detects a 3-D obstacle (W) inhibiting the driving direction of the vehicle (1) based on an image captured by a stereo camera (3) and determines whether the image ahead of the vehicle (1) is in a condition that makes visual perception of the 3-D obstacle (W) difficult. A controller (6) calculates a required alarm working distance (Dw) between the vehicle (1) and the 3D obstacle (W), at which an alarm unit (8) is worked when the vehicle (1) approaches the 3D obstacle (W), and a required brake operating distance (Dn), at which a brake is operated by a brake applying unit (9), based on a traveling speed (Ve) of the vehicle (1).