A level shifter includes a differential input pair circuit, a current mirror circuit, a switching circuit, a first keeper circuit, a second keeper circuit, and an output buffering circuit. The differential input pair circuit is connected with a first node, a second node and a first voltage. The differential input pair circuit receives an input signal and an inverted input signal. The current mirror circuit is connected with a third voltage, and includes a first current output terminal connected with a third node and a second current output terminal generating an output signal. The switching circuit includes a first control terminal receiving the inverted output signal. The second keeper circuit is connected between the third voltage and the second node, and includes a third control terminal receiving the inverted input signal and a fourth control terminal receiving the inverted output signal.