An imaging device with an arithmetic function in which the circuit size is reduced is provided. The imaging device includes a plurality of pixel blocks. Each of the pixel blocks includes N (N is an integer greater than or equal to 1) first circuits, N second circuits, and a third circuit. Each of the first circuits includes a photoelectric conversion device, and the photoelectric conversion device has a function of converting incident light into an electrical signal and has a function of outputting a first signal that is obtained by binarizing the electrical signal to the second circuit. Each of the second circuits has a function of outputting a second signal that is obtained by multiplying the first signal by a weight coefficient to a third circuit. When the N second signals are output to a wiring electrically connected to the third circuit, addition is performed. The first circuit includes a transistor, and an OS transistor is preferably used as the transistor.