An electronic brake system comprising: a hydraulic pressure supply apparatus generating a hydraulic pressure by operating a hydraulic piston by an electrical signal output corresponding to a displacement of a brake pedal and including a first pressure chamber formed at one side of the hydraulic piston movably accommodated in a cylinder block and a second pressure chamber formed at the other side of the hydraulic piston; and a hydraulic control unit including a first hydraulic circuit for controlling the hydraulic pressure transmitted to two wheel cylinders and a second hydraulic circuit for controlling the hydraulic pressure transmitted to two other wheel cylinders, wherein the hydraulic control unit includes a first hydraulic passage communicating with the first pressure chamber, second and third hydraulic passages (212, 213) branched from the first hydraulic passage and connected to the first and second hydraulic circuits (201, 202) respectively, a fourth hydraulic passage communicating with the second pressure chamber, fifth and sixth hydraulic passages (215, 216) branched from and rejoining the fourth hydraulic passage, a seventh hydraulic passage connecting the second hydraulic passage and the third hydraulic passage, an eighth hydraulic passage connecting the second hydraulic passage and the seventh hydraulic passage, and a ninth hydraulic passage connecting a point where the fifth and sixth hydraulic passages (215, 216) rejoin and the seventh or eighth hydraulic passage (217, 218), wherein the hydraulic control unit includes a first valve provided on the second hydraulic passage to control the flow of a pressurized medium, a second valve provided on the third hydraulic passage to control the flow of the pressurized medium, a third valve provided on the fifth hydraulic passage to control the flow of the pressurized medium, a fourth valve provided on the sixth hydraulic passage to control the flow of the pressurized medium, a fifth valve provided on the seventh hydraulic passage to control the flow of the pressurized medium, and a sixth valve provided on the eighth hydraulic passage to control the flow of the pressurized medium. a hydraulic pressure supply apparatus generating a hydraulic pressure by operating a hydraulic piston by an electrical signal output corresponding to a displacement of a brake pedal and including a first pressure chamber formed at one side of the hydraulic piston movably accommodated in a cylinder block and a second pressure chamber formed at the other side of the hydraulic piston; and a hydraulic control unit including a first hydraulic circuit for controlling the hydraulic pressure transmitted to two wheel cylinders and a second hydraulic circuit for controlling the hydraulic pressure transmitted to two other wheel cylinders, wherein the hydraulic control unit includes a first hydraulic passage communicating with the first pressure chamber, second and third hydraulic passages (212, 213) branched from the first hydraulic passage and connected to the first and second hydraulic circuits (201, 202) respectively, a fourth hydraulic passage communicating with the second pressure chamber, fifth and sixth hydraulic passages (215, 216) branched from and rejoining the fourth hydraulic passage, a seventh hydraulic passage connecting the second hydraulic passage and the third hydraulic passage, an eighth hydraulic passage connecting the second hydraulic passage and the seventh hydraulic passage, and a ninth hydraulic passage connecting a point where the fifth and sixth hydraulic passages (215, 216) rejoin and the seventh or eighth hydraulic passage (217, 218), wherein the hydraulic control unit includes a first valve provided on the second hydraulic passage to control the flow of a pressurized medium, a second valve provided on the third hydraulic passage to control the flow of the pressurized medium, a third valve provided on the fifth hydraulic passage to control the flow of the pressurized medium, a fourth valve provided on the sixth hydraulic passage to control the flow of the pressurized medium, a fifth valve provided on the seventh hydraulic passage to control the flow of the pressurized medium, and a sixth valve provided on the eighth hydraulic passage to control the flow of the pressurized medium.