An output buffer including a first differential input stage, a primary output stage, and a secondary output stage is provided herein. The first differential input stage respectively receives a first and a second input signals via a first and a second input terminals. The primary output stage includes a first and a second output stages. The first output stage provides at least one first level voltage according to the first and the second input signals, and the second output stage controlled by the first level voltage drives an output terminal of the output buffer to a target level. The secondary output stage includes a comparator and a third output stage. The comparator compares the induced currents in the first differential input stage, and thereby generates a control voltage. The third output stage controlled by the control voltage drives the output terminal of the output buffer to the target level.