a first block in which a mechanical unit operated mechanically in association with a brake pedal is disposed;

a second block in which an electrical unit electronically operated and controlled by an electronic control unit (ECU) is disposed; and

a connection line configured to hydraulically connect the first block and the second block; wherein

the mechanical unit comprises:

a main reservoir in which a pressurized medium is stored; and

an integrated master cylinder comprising a simulation piston connected to the brake pedal, a simulation chamber whose volume is changed by a displacement of the simulation piston, a master piston connected to the simulation piston, a master chamber whose volume is changed by a displacement of the master piston, and an elastic member provided between the simulation piston and the master piston;

the electrical unit comprises:

a hydraulic pressure supply device configured to generate a hydraulic pressure by operating a hydraulic piston by an electric signal output in response to a displacement of the brake pedal;

a hydraulic control unit including a first hydraulic circuit having two wheel cylinders, a second hydraulic circuit having the other two wheel cylinders, and a plurality of flow paths and valves configured to control a hydraulic pressure transmitted to the first hydraulic circuit and the second hydraulic circuit; and

the ECU;

the connection line comprises:

a first connection line connecting the simulation chamber to the first hydraulic circuit;

a second connection line connecting the master chamber to the second hydraulic circuit; and

a third connection line connecting the main reservoir to the hydraulic pressure supply device and the second hydraulic circuit, respectively,

wherein

the master piston comprises a first master piston and a second master piston,

the master chamber comprises a first master chamber whose volume is changed by a displacement of the first master piston and a second master chamber whose volume is changed by a displacement of the second master piston,

the first master piston is connected to the simulation piston through the elastic member, and

the second master piston is provided between the first master chamber and the second master chamber to be displaceable by a hydraulic pressure of the first master chamber.