Disclosed herein are an electric brake system (1;2;3) and four operating methods thereof. The disclosed electric bake system (1;2;3) may include a master cylinder (20) discharging pressure medium according to a displacement of a brake pedal (10), a simulator (50) providing a sense of brake pedal feel to a driver, a hydraulic supplier (100) generating hydraulic pressure by operating a hydraulic piston (114) in response to an electrical signal output by corresponding to the displacement of the brake pedal (10), and a hydraulic control unit (200) controlling hydraulic pressure of the pressure medium supplied to each wheel cylinder (40) by means of six flow paths (211-216). The disclosed electric brake system (1;2;3) may perform a normal operation mode having a low pressure mode and a high pressure mode, an abnormal operation mode and an inspection mode.