A single input level shifter, which performs a stable level-shifting operation without increasing its area when used with a thin film transistor (“TFT”) having a variety of different characteristics, and includes an intermediate voltage signal providing unit for providing an intermediate voltage signal having a voltage between a supply voltage and an input signal voltage, an inverting unit for receiving the intermediate voltage signal and providing an inverted intermediate voltage signal, and a voltage signal comparing unit for comparing the intermediate voltage signal with the inverted intermediate voltage signal and providing the supply voltage or the ground voltage according to the comparison. A TFT liquid crystal display (“LCD”) device employs the single input level shifter.