A device for quantitatively determining an analyte is provided to conspicuously improve the performance of the quantitative determination. This device is equipped with a flow channel, an analyte detecting unit for capturing and detecting the analyte, and a quantitative measurement unit for quantitatively determining the analyte, wherein a signal generated when the analyte detecting unit has detected the analyte is divided into a plurality of parts in the direction of the flow in the flow channel at the quantitative measurement unit for processing. Also provided are technologies including one for controlling the density of molecules attached to the surface of a solid. In these technologies, when molecules are attached to a substrate, the density of attached molecules is controlled, by having an electrolyte also present in a solution containing the molecules to adjust the screening effect by the electrolyte, and by taking into consideration the effective size of a molecule.