There is provided a vehicle driving support device. The vehicle driving support device according to the present invention calculates a time-to-collision to an obstacle ahead. When the time-to-collision is shorter than a predetermined threshold value, which means the possibility of the collision between the obstacle and a vehicle is determined to be high, and in at least either one of cases in which an engine automatic stop controller automatically stops an engine and in which a brake negative pressure is higher than a set pressure, so that the negative pressure of a brake booster is insufficient, the device outputs a signal to a brake controller so as to start a pump of a brake driver for realizing a prefill function in which a brake pad of each wheel is pressed against a braking surface of a disc rotor.