A level shifter includes a first input circuit, a first load circuit, a second input circuit, and a second load circuit. The first input circuit receives a first input signal and a second input signal that swing between a first high power voltage and a first low power voltage. The first load circuit generates a high voltage, a sub-high voltage, a low voltage, and a sub-low voltage. The second input circuit receives a first voltage pair including the high voltage and the low voltage, and a second voltage pair including the sub-high voltage and the sub-low voltage. The second load circuit generates an output signal that swings between a second high power voltage and a second low power voltage.