A plurality of sensor pixel circuits each including two photodiodes, one accumulation node accumulating charge corresponding to an amount of light, and a read transistor having a control terminal connected to the accumulation node are arranged in a pixel region. In accordance with a clock signal, when a backlight is turned on, a transistor turns on, a current flows through the photodiode, and a potential at the accumulation node drops. When the backlight is turned off, a transistor turns on, a current flows through the photodiode, and the potential at the accumulation node rises. Sensitivity characteristics of the two photodiodes may be changed using the clock signal. The sensor pixel circuit described above is used for detecting a difference between an amount of light to be incident when the backlight is turned on and an amount of light to be incident when the backlight is turned off.