An imaging device that is highly stable to irradiation with radial rays such as X-rays and can inhibit a decrease in electrical characteristics is provided. The imaging device takes an image with radial rays such as X-rays and includes pixel circuits arranged in a matrix and a scintillator overlapping the pixel circuits. The pixel circuits each includes a switching transistor with an extremely small off-state current and a light-receiving element which is configured to convert the radial rays to electrical charges. A gate insulating film of the switching transistor has a stacked structure including a silicon nitride film with a thickness of 100 nm to 400 nm and a silicon oxide film or a silicon oxynitride film with a thickness of 5 nm to 20 nm.