A brake system and a method of controlling the brake system including a pedal master unit, an electric booster unit, a pedal-feel generating unit, and an electric control unit, wherein the pedal master unit includes a master cylinder and an operating rod, the electric booster unit includes a motor, a motor piston, and a gear device-screw shaft combination, the pedal-feel generating unit includes a reaction disk configured to form a pedal feel force (FRD) and a pedal spring arranged to form a pedal feel force (Fspring), and the electric control unit is configured to variably control, in a regenerative braking mode and in a hydraulic braking mode, a ratio of increase to decrease of the pedal feel force (FRD) and a ratio of increase to decrease of the pedal feel force (Fspring).