The present invention provides a data driver on which an operation test can be easily and reliably conducted at the stage of manufacture and for which the testing time can be reduced and a display utilizing the same. A select switch portion 60 is provided for electrically connecting and disconnecting a ladder resistor portion 56 and selector portions 58. At the ends of wiring of grayscale voltage lines l1 through l64 opposite to the ladder resistor portion 56, there is provided a state setting circuit 62 which sets each of the grayscale lines l1 through l64 at a “High” level or a “Low” level or which sets the ends of the grayscale voltage lines l1 through l64 in a high impedance state. The state setting circuit 62 is further connected to a testing control portion 64 incorporating a shift register which operates in synchronism with a test clock TST-CLK.