A level shifter removes delay, which is generated at the time of transition of an input signal level, by adjusting a size of NMOS transistors to perform pull-down and pull-up operations. The level shifter includes a coupling unit for setting up a voltage level of a first node according to a voltage level of an input signal, a first buffer for transferring an output signal by buffering a signal from the first node, and a driving unit configured to receive the input signal and the output signal and drive the first node.