A display device including: a display panel; a first substrate attached to a side of the display panel; and a second substrate attached to a side of the first substrate, wherein the display panel includes a first panel test pad and a second panel test pad, the first substrate includes a 1-1 circuit test lead overlapping and connected to the first panel test pad, a 1-2 circuit test lead overlapping and connected to the second panel test pad, a 2-1 circuit test lead overlapping and connected to the second substrate, a 1-1 test lead line connected to the 1-1 circuit test lead, a 1-2 test lead line connected to the 1-2 circuit test lead, and a first test lead line connected to the 2-1 circuit test lead, and the 1-1 test lead line and the 1-2 test lead line are connected to the first test lead line.