Because a charge injection type “two level” CCD image sensor needs metal contact to carry signal charge from its photoelectrical conversion layer to its storage diode, this type of sensor has a peculiar random noise generated in its picture cells. This noise has been studied from the view-point of electron emission from the storage diode, and the noise value obtained by measuring a 1-inch 2-million pixel image sensor corresponds to the analytically derived noise. We expect that the smaller a picture cell is, the less the noise value is.