The present disclosure provides an electric booster comprising: a motor piston configured to be moved by a motor; an operating rod configured to be moved in a direction parallel to a moving direction of the motor piston; a reaction disc configured to be pressed and moved by at least one of the motor piston and the operating rod; a master cylinder configured to generate a hydraulic pressure as the reaction disc moves; and a control unit controlling the operation of the motor, wherein the control unit receives the stroke of the brake pedal, calculates a required hydraulic braking force and a required stepping force based on the pedal stroke, and determines a required displacement of the motor piston for generating the required hydraulic braking force and the required stepping force using a contact area between the operating rod and the reaction disc.