It is an object to provide a touch panel with high precision, high-speed operation, and low power consumption, which is caused by reduction of power consumption in an A/D converter circuit is reduced. In the touch panel in which a photo sensor is included in a pixel and an A/D converter circuit is provided every one column or a plurality of columns of the pixels, a control signal of the A/D converter circuit is sequentially supplied by a shift register included in an ADC (A/D converter circuit) control circuit, and respective periods when the plurality of A/D converter circuits operates are not overlap with each other. Accordingly, the number of A/D converter circuits which operate at the same time is decreased, and instantaneous power consumption in the A/D converter circuit is decreased.