Abstract: Disclosed is an apparatus and a method, in which gray levels are realized in such a manner that a pixel is supplied with a constant current instead of a voltage and charging duration (required for inputting data until a gate is turned on/off) is time-divided by the number of gray levels to be realized. The apparatus includes a current supplier for supplying a current filling a pixel, a buffer for latching display data, an adder for adding currently-input display data and display data latched the buffer, a pulse generator for receiving data outputted from the adder and delivering a switch-on pulse having a pulse width corresponding to the outputted data to the current supplier, and a controller for controlling the current supplier, the adder, and the pulse generator.