A brake system including a main body having a first main chamber and a second main chamber divided by a main piston, a motor configured to move the main piston forward and move the main piston rearward, a first traction control valve installed in a first flow path, a second traction control valve installed in a second flow path, and a controller configured to control the motor, the first traction control valve, and the second traction control valve. When an anti-lock brake system (ABS) starting pressure is lower than an ABS critical value, the controller performs a low-pressure forward movement connection control that closes the first traction control valve and the second traction control valve, and moves the main piston forward to increase a first hydraulic pressure in the second main chamber.