1. An apparatus for detecting an amount of an object of analysis by using a sensor element, the sensor element of a contact lens shape on an eye, comprising: a lens barrel which comprises: a light source for illuminating the sensor element, an image pickup device for picking up an image of an iris, and a light-shielding member for preventing external light from entering inside of the lens barrel; wherein the sensor element includes a sensor portion comprised of a substrate for fixing a molecule capable of selectively capturing the object of analysis and a code portion for identifying a subject person; and wherein (i) an image of the code portion is picked up by the image pickup device, illuminating the code portion with the light source, (ii) an image of an iris is picked up by the image pickup device, illuminating the eye with the light source (iii) and the image of the code portion and the image of the iris are compared to each other to identify the subject person; wherein, with a reagent comprised of a fluorescent substance present on said sensor element, the fluorescent substance executing a competing reaction with the object of analysis, and the light source illuminating said sensor element, the amount of the object of analysis captured by the capturing molecule is detected by an amount of fluorescence of the fluorescent substance, and wherein the sensor portion is irradiated with light having a wavelength different from the wavelength of light with which the code portion and the iris are irradiated to detect the amount of the object of analysis when the subject person is identified from a sensor portion for identifying.