An imaging element which is capable of obtaining a piece of image data by performing light exposure plural times is provided. In addition, an imaging element which is capable of obtaining image data with little noise is provided. Furthermore, an imaging device with reduced power consumption is provided. In an imaging element including a pixel, the pixel includes a photodiode, a transistor including an oxide semiconductor layer, a diode, and a charge retention portion. The polarity of an electrode of the photodiode which is connected to the transistor is the same as that of an electrode of the diode which is connected to the transistor.