An imaging device having a memory function is provided. Alternatively, an imaging device suitable for taking images of a moving object is provided. The imaging device includes a first to third layers; the second layer is provided between the first and the third layer; the first layer includes a photoelectric conversion device; the second layer includes a first and a second circuit; the third layer includes a third and a fourth circuit; the first circuit and the photoelectric conversion device have a function of generating imaging data; the third circuit has a function of reading the imaging data; the second circuit has a function of storing the imaging data read by the third circuit; the fourth circuit has a function of reading the imaging data stored in the second circuit; and the first circuit and the second circuit include a transistor including a metal oxide in a channel formation region.