An electronic brake system comprising: a reservoir in which a pressurizing medium is stored; an integrated master cylinder including a master chamber , a master piston provided in the master chamber and configured to be displaced by a brake pedal ; a liquid pressure supply device configured to generate a liquid pressure by operating a hydraulic piston according to an electrical signal being output in response to a displacement of the brake pedal ; and a hydraulic control unit having a first hydraulic circuit for controlling a liquid pressure transferred to two wheel cylinders and a second hydraulic circuit for controlling a liquid pressure transferred to other two wheel cylinders , characterised in that the integrated master cylinder further comprises: first and second simulation chambers , a reaction piston provided in the first simulation chamber and configured to be displaced by a liquid pressure of a pressurizing medium accommodated in the master chamber , a damping piston provided in the second simulation chamber and configured to be displaced by the displacement of the reaction piston , and an elastic member provided between the reaction piston and the damping piston ; a simulation fluid path configured to communicate the first simulation chamber with the second simulation chamber ; and a simulator valve provided on the simulation fluid path and configured to control a flow of a pressurizing medium. a reservoir in which a pressurizing medium is stored; an integrated master cylinder including a master chamber , a master piston provided in the master chamber and configured to be displaced by a brake pedal ; a liquid pressure supply device configured to generate a liquid pressure by operating a hydraulic piston according to an electrical signal being output in response to a displacement of the brake pedal ; and a hydraulic control unit having a first hydraulic circuit for controlling a liquid pressure transferred to two wheel cylinders and a second hydraulic circuit for controlling a liquid pressure transferred to other two wheel cylinders , characterised in that the integrated master cylinder further comprises: first and second simulation chambers , a reaction piston provided in the first simulation chamber and configured to be displaced by a liquid pressure of a pressurizing medium accommodated in the master chamber , a damping piston provided in the second simulation chamber and configured to be displaced by the displacement of the reaction piston , and an elastic member provided between the reaction piston and the damping piston ; a simulation fluid path configured to communicate the first simulation chamber with the second simulation chamber ; and a simulator valve provided on the simulation fluid path and configured to control a flow of a pressurizing medium. first and second simulation chambers , a reaction piston provided in the first simulation chamber and configured to be displaced by a liquid pressure of a pressurizing medium accommodated in the master chamber , a damping piston provided in the second simulation chamber and configured to be displaced by the displacement of the reaction piston , and an elastic member provided between the reaction piston and the damping piston ; a simulation fluid path configured to communicate the first simulation chamber with the second simulation chamber ; and a simulator valve provided on the simulation fluid path and configured to control a flow of a pressurizing medium. <EOS>