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 (41, 42) and a second hydraulic circuit for controlling a liquid pressure transferred to other two wheel cylinders (43, 44), characterised in that the integrated master cylinder further comprises: first and second simulation chambers (22a, 23a), 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 (41, 42) and a second hydraulic circuit for controlling a liquid pressure transferred to other two wheel cylinders (43, 44), characterised in that the integrated master cylinder further comprises: first and second simulation chambers (22a, 23a), 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 (22a, 23a), 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.