A liquid crystal material is prevented from being degraded by a voltage to control the shift of the threshold voltage which is applied to a back gate on the same conductive film as a pixel electrode. A liquid crystal display device includes a pixel circuit including a pixel electrode which applies an electric field to a liquid crystal layer; and a driver circuit including a transistor including a first gate and a second gate with a semiconductor film interposed therebetween. The transistor overlaps with the liquid crystal layer. A signal for controlling on/off of the transistor is input to the first gate. A signal for applying a first voltage is input to the second gate in a gate line selection period. A signal for alternately applying the first voltage and a second voltage is input to the second gate in a vertical retrace period.