A pad printing device for printing a window of a display device includes a pad to transfer ink to the window. The pad includes a printing portion to transfer the ink to the window by being pressed against the window and a body portion disposed on the printing portion and to apply a pressure to the printing portion. A hardness of the printing portion is less than a hardness of the body portion, and a sidewall of a portion of the pad where the printing portion contacts the body portion is substantially perpendicular to the window.