A hydraulic brake device for a vehicle includes a master piston, an auxiliary piston having first and second pistons, and an assisting device for assisting actuation of the master piston through the auxiliary piston. The brake pressure increase gradient in the assisting operation of the assisting device after the assisting output force of the assisting device reaches a maximum value is the same as the brake pressure increase gradient in the assisting operation of the assisting device before the assisting output force of the assisting device reaches the maximum value because the second piston of the auxiliary piston includes a large diameter portion possessing a diameter that is the same as the diameter of the master piston.