According to one embodiment, a wiring substrate includes a pad group of a first pad to supply a power source voltage of low level, a second pad to supply a power source voltage of high level, and a third pad to supply a necessary signal for displaying an image, a common line, a first connection line to connect the first pad with the common line, a second connection line to connect the second pad with the common line, and a third connection line to connect the third pad with the common line, wherein the first connection line and the second connection line are formed of polysilicon in which no impurity is doped, and the third connection line and the common line are formed of polysilicon in which an impurity is doped.