To prevent vehicle behavior from being disturbed due to assistant braking force, concerning an assistant brake control device for vehicle generating assistant braking force by contacting assistant brake members with the road surface on a low friction coefficient road.

Assistant brake mechanisms 10FR, 10FL are provided right and left symmetrically against the center line of a vehicle. When a road during running is a fixed low friction coefficient road and the vehicle is required to brake, the assistant brake mechanisms 10FR, 10FL are operated so that cylindrical bodies 12FR, 12FL are grounded. A yaw rate sensor 38 detecting the yaw rate γ of the vehicle is provided. When change Δγ over a fixed value is generated in the yaw rate γ accompanying operation of the assistant brake mechanisms 10FR, 10FL, the assistant brake mechanisms 10FR, 10FL are prohibited to operate.