A display driver device includes a timing controller, a display driver integrated circuit, a flexible printed circuit board, a connection line, and a test line. The timing controller includes an output pad unit. The display driver integrated circuit includes an input pad unit. The connection line is formed at the flexible printed circuit board to electrically connect the input pad unit with the output pad unit. The test line is formed at the flexible printed circuit board, and is used to provide a test signal to the input pad unit. The display driver device operates in a normal mode or operates in the test mode based on a test mode signal.