A vehicle having a vehicle brake system, comprising: an input device which receives an operator's brake operation; an electric brake actuator which generates a brake hydraulic pressure based on an electric signal according to at least the brake operation; a vehicle behavior-stabilizing device which assists vehicle behavior stabilization based on the brake hydraulic pressure generated in the electric brake actuator; and a stroke simulator giving a brake operator a simulated operation reaction force; wherein the input device, the electric brake actuator, and the vehicle behavior-stabilizing device are connected via piping (22a, 22d) which transports brake fluid, wherein the input device has a housing which includes a master cylinder capable of generating a hydraulic pressure according to an input through operation of the brake operator in wheel cylinders at a time of an abnormal condition of the electric brake actuator; and two output connection ports (20a, 20b) of the master cylinder are connected via pipes with branches on piping connecting the vehicle behavior-stabilizing device and the electric brake actuator; the master cylinder extending in a front-rear direction of the vehicle; and the input device, the electric brake actuator, and the vehicle behavior-stabilizing device are separately disposed from one another in a room for structures, the room being partitioned in front of a dashboard; the stroke simulator is disposed in parallel to and in communication with the master cylinder, so that the stroke simulator and the master cylinder are integrated; characterised in that first and second bosses (37a, 37b) project forward of the input device, and third and fourth bosses (39a, 39b) both project either right- or left-or up- or downward of the input device, wherein these first to fourth bosses (37a, 37b, 39a, 39b) have flat working surfaces (37a1, 37b1) formed beforehand at a plurality of locations in the housing of the input device; and that the two output connection ports (20a, 20b) are produced in the flat working surfaces (37a1, 37b1) of a selected pair of the first and second or third and fourth bosses (37a, 37b, 39a,39b). an input device which receives an operator's brake operation; an electric brake actuator which generates a brake hydraulic pressure based on an electric signal according to at least the brake operation; a vehicle behavior-stabilizing device which assists vehicle behavior stabilization based on the brake hydraulic pressure generated in the electric brake actuator; and a stroke simulator giving a brake operator a simulated operation reaction force; wherein the input device, the electric brake actuator, and the vehicle behavior-stabilizing device are connected via piping (22a, 22d) which transports brake fluid, wherein the input device has a housing which includes a master cylinder capable of generating a hydraulic pressure according to an input through operation of the brake operator in wheel cylinders at a time of an abnormal condition of the electric brake actuator; and two output connection ports (20a, 20b) of the master cylinder are connected via pipes with branches on piping connecting the vehicle behavior-stabilizing device and the electric brake actuator; the master cylinder extending in a front-rear direction of the vehicle; and the input device, the electric brake actuator, and the vehicle behavior-stabilizing device are separately disposed from one another in a room for structures, the room being partitioned in front of a dashboard; the stroke simulator is disposed in parallel to and in communication with the master cylinder, so that the stroke simulator and the master cylinder are integrated; characterised in that first and second bosses (37a, 37b) project forward of the input device, and third and fourth bosses (39a, 39b) both project either right- or left-or up- or downward of the input device, wherein these first to fourth bosses (37a, 37b, 39a, 39b) have flat working surfaces (37a1, 37b1) formed beforehand at a plurality of locations in the housing of the input device; and that the two output connection ports (20a, 20b) are produced in the flat working surfaces (37a1, 37b1) of a selected pair of the first and second or third and fourth bosses (37a, 37b, 39a,39b).