A circuit which detects an output current from a pixel and an output current from an input device, and converts the output current into data is provided. The current detection circuit includes an integrator circuit, a comparator, a counter, and a latch. The integrator circuit integrates the potential of a first signal during a period determined by a second signal and outputting it as a third signal. The comparator compares the potential of the third signal with a first potential and outputting a fourth signal. The counter outputs the number of pulses included in a fifth signal as a sixth signal during a period determined by the fourth signal. The latch holds the sixth signal. The integrator circuit preferably further includes an operational amplifier and some capacitors. The first signal is supplied from a pixel included in a display device or an input portion included in an input device.