Disclosed is an electronic brake system including: a reservoir to store oil; a master cylinder connected to the reservoir and including first and second master chambers and first and second piston provided in the first and second master chambers, respectively, to discharge the oil according to an pedal effort of a brake pedal; a hydraulic pressure generating apparatus provided on at least one of a first reservoir passage connecting the reservoir and the first master chamber and a second reservoir passage connecting the reservoir and the second master chamber; a hydraulic pressure supply apparatus operated by an electrical signal to generate a hydraulic pressure and connected to the master cylinder; and a hydraulic pressure control unit transmitting alternatively the hydraulic pressure discharged from the hydraulic pressure generating apparatus or the hydraulic pressure supply apparatus to a wheel cylinder provided on each of four wheels.